Canadians died in the September 11 attack. It is the responsibility of any government to protect it's citizens, regardless of where they were when it happened.
The September 11 attacks are not an isolated incident.
Of course it is the responsibility of a government to protect it's citizens. Should it avenge their deaths also? Sure, most folks have no problem with that premise. It gets shaky though when the 9/11 attacks were an inside job. Do you go after the US? You can't really. So as a politician you just play along, until the people wise up and tell you to stop. But I don't think you're going to see that anytime soon.
If they keep trying to scare us (think Orwell's Goldstein), then there is always the seed of doubt "gee, what if there really are terrorists?", or worse yet "what if these 9/11 clowns decide to blow some of us up if we don't go along" sort of thing. It's a lose/lose situation.
We will need a person of the stature of a Mohatmas Ghandi to stand up to these Americans and say, no, we are no longer playing along, and we will no longer sacrifice Canadian children to your deceitful invasions.