"Al Qaeda has attacked Britain, the US, and Spain, and has advocated the destruction of the entire Western world, yet you think they just wouldn't bother with Canada?"
They haven't yet and since they attacked you first they obviously aren't afraid of American retaliation. Now before you say something about the war in Iraq preventing them from getting here keep in mind that even in areas like Iraq anyone physically capable of boarding a plane can get into Canada.
"By the way, you still haven't addressed the fact that the lack of a threat to Canada is proof of the success of the program."
Ok I'm gonna rip off the Simpsons here. If I claim a rock keeps tigers away is the lack of tigers proof the rock works?
"when were the last major terrorist attacks on Canada?"
October Crisis 1970 series of attacks by the FLQ (Front de Liberation du Quebec) wanted Quebec Sovereignity and kidnapped English government officials, blew up cars, mailboxes etc. They were efficiently put down by Prime Minister Pierre Trudeau through enacting the War Time Measures Act which essentially declared martial law.
"Does Canada even have any major terrorist groups of its own"
Aside from the FLQ I don't believe so and I don't think they exist anymore
There are 10 kinds of people in this world, those who understand binary and those who don't.