Canada vs. US Warranty...
Camera manufacturers can be very picky about authorized dealers vs. warranties. For instance, here in the US, some retailers sell 'Grey Market' gear. It's usually exactly the same as the normal gear (made in the same factory, etc), but it doesn't carry the same warranty. The benefit is that they're a usually a bit cheaper, but there's no warranty on it.
Nikon/Canon USA is a seperate business entity from Nikon/Canon Canada, and so the warranties are different and probably not cross-supported. I would email and/or call the companies directly to confirm that.
I would assume that if you bought a USA-Warranty camera, that you would need to send it back to the US service department, should you have problems.
Edit:
this seems to be in agreement with what I said, at least for Nikon.
