If you are comfortable doing your own upgrades, check out:
http://www.otherworldcomputing.com/
They have great prices, and tons of different upgrade options for all sorts of Macs. The shipping too Canada wasn't too steep either, from what I remember. Even so, watch out for UPS... the brokerage fees can be brutal depending on the level of shipping you choose.
Typically, I have purchases delivered to
http://www.usaddressinc.com and pick them up on my own to take advantage of free shipping within the US, or avoid excessively expensive shipping costs to Canada.
I'm all for supporting local businesses, but I find that with many Mac upgrades, Mac specific stores often charge a premium for a component that would also work in any PC and could be purchased elsewhere for way less money.