Ive just bought a new computer, so Ive done the research on stores and such. For the most part, Ive found NCIX to be the cheapest, with Canada Computers good for a few items as well. Great part about NCIX, they price match, so you can get deals that they might not normally have. Nice thing about Canada Computers though, $10 flat rate shipping, which might save you some money on a case. Also, depending on your province, you can dodge the provincial sales tax from at least one of the stores, which adds up on a large purchase.
As for the computer itself, Im guessing you want to run it at stock and such, no overclocking? I imagine you could get a C2D 6300, decent motherboard (maybe a gigabyte DS3, or something lower than that), 250GB HD, DVD burner, case w/included PSU and such and a 7600 GT video card for about that budget. Im afraid I cant price it right now, but the NCIX pc builder is good to play around with.