Be aware that they're increasingly starting to verify that your cc has a US billing address.
If that happens, that's fine it just means the purchase wont be able to go through and no loss. The problem scenario would be purchasing something and then being unable to redeem it, which technically seems unlikely between Canada<->US, but if that occurred I'm sure they would simply refund the purchase with an appropriate polite customer service request so I'm not particularly worried until either I have an actual problem personally or I see some other Canadian describe a story where they got burned out of money. Haven't seen that happen yet though in several years time so it's still worth trying IMHO. Should they manage to find a way to lock out Canadians, that is their loss as our business wills imply just go to Greenman Gaming, Gamersgate, Steam directly, Humble Store, Indie Gala Store, Bundlestars Store, and <insert 1000 other Steam resellers here>, so it is kind of stupid to prevent Canadians from shopping at amazon.com for games really. Incredibly stupid in my eyes. I actually have accounts at American financial institutions also with gobs of USD, and could get a US credit card in my name and I could easily have a friend's address used if I wanted to continue the game, but there's a point where someone puts up walls and barriers of doing business with me where I just say "ok, you don't want my money, no problem I'll give it to someone who does" though. :) For now I'll keep using the aforementioned trick though as long as it continues to work, not that I shop at amazon.com often mind you. :)