I don't know if Canada would be a priority for al Qaeda,
ceteris paribus. But the real al Qaeda of today finds its reach shortened and its teeth blunted by a vigorous and ongoing campaign to engage its elements in the Middle East. As such it must strike where it can, if at all.
The question is whether the assets it has in place in Canada (1) are sufficient to the task, and (2) have a target in mind that will benefit al Qaeda more than cost it. But as time goes on it becomes more and more important to al Qaeda to assert itself somewhere or lose the terror it has tried so hard to make its name evoke. That means that it may just take whatever it feels it can. That is something to worry about whether you're Canadian or American.
It really doesn't make political sense for al-Qaida to attack Canada. It makes more sense for them to play on the anti-American, anti-Iraq war sentiments and nurture the divisions between the France/Germany/Canada/UN bloc and the and US/UK/AU/Italy/Poland alliance.
That's not to say that some overzealous Imam might do something irrational in Canada. But that would be couterprodutive and probably trigger a Dutch-like wake up call to the Canadians who think they're immunized against Islamofacists (and missiles too, because they're so darned 'nice'. ). Al-Qaida has it's hands full right now, it wouldn't make sense to add to turn Canadian government opinion against them.