Off the top of my head, here are some thoughts. I don't know much about American med schools-- just that the more I hear about them from SDN, the gladder I am, and the luckier I feel, that I'm here instead. 🙂
Advantages of Canadian schools:
-cheaper tuition, and potentially student loan support from your province of residence (if you have one)
-cheaper/safer cities, generally, than the States
-(generally) smaller class sizes
-a smaller national medical community-- in every hospital in Canada, there are alumni from my med school, and people who know my profs, or even people who trained with my parents or are related to my classmates or have a million and one other potential connections with me already (lots of networking opportunities-- and it also means that you're not too far removed from even the most important people in the profession here) *hums "It's a Small World"*
Advantages of American schools:
-there are more "big name" schools (if you can get into them/afford them)
-greater possibility of having 'international' names as faculty members or working in the same hospital
-I think the programs might be better funded, in terms of resources & facilities
-more options (and more diverse options) for residencies
-warmer weather
-more schools, in general, to choose from, so you can find one that's perfect for you
As far as working outside of North America eventually, I believe Canadian-trained MDs are regarded as equivalent to Americans pretty much all over the world, unless you count on the advantage of having gone to a hugely famous American school (which, let's face it, is a much bigger deal within the States than outside).
I know several Canadian docs who have emigrated to work in England or continental Europe. And all the opportunities for working in underdeveloped countries are identical.
I guess I'll never consider going back to the U.S now if this trend continues! 
