I HATE thecamerastore.com with a burning passion.
Their prices are ridiculous, their selection is ok at best and their customer service sucks balls. When I was buying my 70-200 (back when the CDN dollar was worth MORE than the US dollar, I called them up and here's how the convo went:
me: "hey, I found the 70-200 for $549 in the US, but I'd love to support a Canadian company instead. How close can you come to it?"
camerastore: "uhh...how much do we have it for?"
me: "$642.79"
camerastore: "well...I can go as low as $642.79 ... how's that?"
That little smartass quip lost them my business for ever. (I ended up ordering the 70-200 along with a Tamron 17-50 f2.8, well over $1K worth of equipment from the American company that day and laughed all the way to the bank).
Aside from that...I use:
http://www.bhphotovideo.com (they're not the best, but sometimes they have good deals)
http://www.sigma4less.com (I've ordered a few things from there...their customer service isn't the greatest, but their prices rule). Coincidentally, I'm ordering a Tamron TC from them tomorrow.
amazon would be good, but the US site doesn't ship to Canada and the Canadian site sucks for selection.
I find Adorama's prices to be high (they include free shipping in the States, so they jack their prices...so us Canadians get hit twice).