Maybe not so stupid. I have only bought one card (1600) in the States and it DID NOT work. Kept saying the code was invalid, but when I called MS support, they said the code should work. So there actually could be something that keeps an American card from working on a Canadian XBL account. I got the card on sale and to try and exchange it would have been a big hassle, so I never got another one. I really don't know if this was a one-off occurrence or not, just be aware.