Since the box is unopened, they should let you trade it for an English version without any trouble.
Guess what? I strolled over to Futureshop and explained yhe situation. They refused to take back the "unopened" french version Win 7 because it was more than 30 days since the purchase. Talked to the manager but he wouldn't budge at all. I guess I'm stuck on having to install the french version after all... First I'll give Microsoft a call to see what if I can use the french CD key on the english version.