Getting stuff shipped out of the US is really expensive. Your best bet for stores that ship to Canada are stores that are in Canada. There aren't a ton of good ones, but here are three:
Vibe Computers
Bigfoot Computers (mostly a modding store)
Tiger Direct
Tiger Direct actually ships stuff from the states to their Canadian place, but because of the way they have it set up it is just like buying from a Canadian company, there are no duties, etc.
Check out
RedFlagDeals for Canadian deals on computer stuff and more.
Hope this helps