I touched on this in a previous post about where to buy camera equipment in Toronto, but I've gotten other questions about buying gear (especially used) from the US.
Let me point out again, you pay no duty whatever on camera equipment purchased from the US and shipped to Canada. You will have to pay PST and GST and cover the exchange of course but when it comes to used equipment you'll still usually save cash, and sometimes quite a lot of cash, by buying stateside.
If you're worried about buying used, it's actually a much better value for your money than buying new. Almost all my lenses and most of my cameras were bought used. A used lens works just as well as a new one.
As far as specific outlets, I'd recommend both B&H Photo and Adorama who are both honest and quite conservative when it comes to their grading system on equipment. Check them out.
