As I've previously written, Canada is a land of immigrants and it is a testament to our immigration system and safeguards that immigrants that choose this country don't increase crime and may in fact suppress it. The jury is still out on the economic costs to welcoming immigrants and it's clear that we need to improve the outcomes of those that come to this country because it's getting longer for them to achieve parity with native born Canadians. That being said, recent immigrants are still holding their own, and in the words of John Ivison of the National Post:
The employment rate for foreign-born men was higher than for native-born men, a statistic that gives the lie to the popular image of the immigrant welfare scrounger.
But, despite the positive impact immigrants have made to this country, the fact of the matter is that some have been able to circumvent the safeguards in our immigration system meant to keep liars, criminals and terrorists out. Our system is not perfect and many are obtaining status that they don't deserve. A recent auditor general's report which reviewed a tiny sample of grants of citizenship outlined the shortcomings of one part of our immigration system. I discussed that report on CBC which can be heard here.
It doesn't take a genius or a criminal mastermind to do an end run around our system since so much of it depends on self-report and documents from countries were document fraud is common-place. The enforcers, those that uphold our immigration system are stymied by the system ("this is the way we do things") and by the sheer numbers (and processing targets) and frankly they are constrained by limited resources (despite all the tough talk from politicians of all stripes).
Prevention remains the best cure. After the fact attempts require firstly detection and then deportation which is hampered (as it should be) by due process.
One way that individuals get to Canada and hide a problematic past is to use false travel documents and commit identity fraud (and simply lie to immigration officers). One particularly strange and compelling case is that of Indian national Parminder Singh Saini who was convicted as a terrorist by a Pakistani court after he and his associates from the All India Sikh Students Federation hijacked an Air India flight to Delhi, forcing it to land in Lahore, Pakistan instead. Saini discharged a firearm in the commission of the offence, and his compatriots injured crew members with their kirpans, threatened and intimidated them for over 20 hours. The Toronto Star article on this case can be found here:
On July 5, 1984, when he was 21, he and four accomplices in the militant All India Sikh Students Federation boarded an Air India flight to Delhi from the northern city of Srinagar.
Twenty minutes after takeoff, he and another man stood up. They pushed aside a female attendant, walked to the front of the plane and Saini - in full view of passengers - raised a handgun to the head of a male attendant and fired.
“(The bullet) did not hit him,” the trial judge later wrote in a 184-page judgment, “but there is little doubt that the object of Parminder Singh (Saini).....was to intimidate and terrorize the crew members and the passengers.”
At the cockpit door, Saini fired two or three more shots - risking the plane’s destruction, the court judgment said. One bullet pierced the door, striking the flight engineer in the back, not seriously. Other hijackers beat and stabbed two other crew members with kirpan daggers.
Sentenced initially to death (by hanging, the apparently preferred execution method of South Asia) he was released by the Bhutto government after serving 10 years and given one month to go to a country of his choice. Not surprisingly, he did not pick India, the country of his birth. Instead, Saini chose to enter Canada in January 1995 with a false Afghan passport as "Balbir Singh" and made a false refugee claim. This allowed him to work and the good character hearing decision of the Law Society of Upper Canada indicates that he continued this "identity charade" for almost a year.
Unfortunately for Saini, CSIS soon detected the fraud and after a hearing before the Immigration and Refugee Board he was found to be inadmissible to Canada. He was also found to be a danger to the public. Saini then fought for almost a decade-and-half to remain in this country. Those efforts included an application under humanitarian and compassionate grounds which was also refused. In the meantime, as is to be expected, he went on with his life.
His "long and strange" journey from terrorist to Canadian law graduate is outlined here. His remarkable sojourn in this country saw him detained for three years; being found a danger to the public; getting released; going to university, graduating with three degrees, including a professional degree and working with one of the preeminent immigration lawyers of the country.
In his efforts to remain here Saini proffered his pardon from Pakistan as evidence of his rehabilitation. That pardon got short shrift from the Federal Court of Appeal:
... It is clear that hijacking is considered to be among the most serious of criminal offences. Hijacking may combine, in one act, numerous offences including kidnapping, unlawful confinement, theft, assault, extortion, and potentially murder. It entails the violation of individual human rights such as the right to life, personal security and freedom of movement. ... Hijacking is not the mere seizure of an aircraft for its own sake; it exploits control over the aircraft “as a weapon of psychological coercion and extortion directed against governments.” … Moreover, the victims of this crime are not limited to those persons unfortunate enough to be physically affected, nor are the effects of hijacking limited to one government. Hijacking terrorizes all nations and society as a whole.
In our view, the gravity of the offence can and should be considered when deciding whether or not to give effect to a foreign pardon. Even if the Pakistani legal system were similar, and even if the pardon were given under a law similar to Canadian law, the conviction in this case was for an offence so abhorrent to Canadians, and arguably so terrifying to the rest of the civilized world, that our Court is not required to respect a foreign pardon of such an offence.
Canada (Minister of Citizenship and Immigration) v. Saini, 2001 FCA 311 (CanLII),  F.C.J No. 1577, Para. 43-44
His application for a law license was refused by the Law Society of Upper Canada despite the passage of time and the support of numerous individuals here in Canada. The decision can be read here:
While Applicant has shown an ability to obtain university degrees and has impressed a number of people, we are still left with a number of serious concerns. In view of: the seriousness of the crime of hijacking; the deception after landing in Canada; the state of the immigration applications, including the fact that he is still described as being a person of danger to the public; and the uncertainty with respect to his good character at this time, the Panel do not find that the Applicant has met the onus of proving, on a balance of probabilities, that he is now of good character.
While Saini expressed remorse over his (leading) role in the terrorist act, he seemed almost blasé about lying to immigration authorities in this country:
 Although Mr. Saini expressed remorse for the hijacking, he passed off the deception of immigration authorities and his own lawyer, as something that everyone does and therefore should not be criticized. ...
I think Saini might be partly right; deception of immigration authorities is something that many do. But that doesn't mean it's justified - and as someone that obtained legal education and sought admission into the profession of law, he should know that.
It took 15 years, numerous hearings and applications, a number of appearances before the Federal Court and Federal Court of Appeal but Saini was finally deported in early 2010 after the Federal Court again ruled against him. Escorted by CBSA officers, Saini was returned to his country of nationality. His legal troubles continue there, as this article from the Hindustan Times indicate.
Any reform of the existing system should not depend on self-report or suspect documents from countries that traffic in fraudulent documents, that have elevated fraud to an art form. Interviewing every applicant just separates the good liars from the bad. Any criminal or terrorist with an IQ of room temperature will be able to pass Kellie Leitch's proposed Canadian Values Interview Exam.
Any meaningful reform will rely more on objective, reliable, third party information. The increasing use of biometrics, facial recognition technology, artificial intelligence and data mining and the sharing of information between countries (particularly the Five Eyes) will likely reduce the incidence of individuals coming into Canada with false travel documents and false identities. That is well and good but how many are here that simply didn't get caught?