Suppose it was the CN tower in Toronto that was attacked. It wasn't a target of opportunity as they say, but Canadians were specifically targeted. In New York they destroyed many square blocks of the most expensive real estate in the US. Who knows, lets say most of down town Toronto is destroyed. Do you think Canada would be the same place it is today?
OK, let's suppose that they had attacked the CN Tower in TO. Here's how I would have handled it if I were the Canadian government:
1. Find out who is responsible. If the guilty all died in the crash, well then that would have been the end of the story. If not, then we find out where the rest of the guilty are.
2. If the rest of the guilty are in Canada, we arrest them. If not, we request extradition. Let's suppose that it was Bin Laden in Afghanistan.
3. If the other country refuses extradition, we request permission from the UN to take him by force. The Un would likely have approved, seeing that they did approve in the US case.
4. Whether approval is given or not, Canada takes security measures at its ports of entry to protect itself against future attacks.
5. If approval for an attack is given, find out how likely it would be to find Bin Laden in Afghanistan. If the chances are pretty good, we attack. If not, we keep the UN's permission to attack folded neetly in our pocket ready to pull it out at any time should the chance to capture Bin Laden become reasonably good. Nothing like a surprise attack while his guard is down.
6. We don't start illegal wars in Iraq on trumped up charges against the wishes of the international community.
Had we gone about that way, there would have been no war in Iraq, and maybe a war in Afghanistan. In the event of a war in Afghanistan, it would have been a quick and decicive war with the clear and explicit objective of capturing Bin Ladin, and launched only once we believed there was a good chance of success. Of course we could have miscalculated, gone in and failed to capture Bin Laden. But as soon as it should become clear that it's not likley to be a success, swallow our pride and pul out. That's just how I would have handled it I think.