No idea, but if Apple was smart they would work hard on bringing this service not only to Canada but to other countries as well outside of the great nation of "U.S.A." as there are a lot of other countries where they could gain much added revenue (and market share) from offering this service.
Plus by keeping it solely in the U.S., they take the risk of losing to other companies that are looking to break into the digital distribution of music by offering them a massive array of countries who can buy music online and not just the U.S.
Hopefully though, because I know I have credit card just itching to get into the world of "1 click shopping"