I live in Southern Ontario. I like to use NCIX and CanadaComputers. Canada Computers has a lot of retail outlets with prices that are comparable to NCIX. They also do price match!
NCIX is great, it always has sales weekly.
OP you can also try PC Part Picker: http://pcpartpicker.com/ca/
as malbluff has said, the link I provided is the direct link to the Canadian version.