Which GPU should I choose, and is Canadian Computers trustworthy?

I'd personally go for Canadian Computers! I've shopped there for years without any fraud problems. You can even ask to open the box when you pay, just to check it out. Just keep in mind they have a restocking fee for returns, so be careful about that.

Definitely avoid buying from their website if you can. I've had some bad experiences; they can try to dodge warranties. I got repackaged motherboards twice, and I know others who got their credit card blocked after shopping online because of their payment process. For the GPUs, both are solid choices, but I'd say Sapphire has a better reputation for warranty.

Think about what you might need to return to Canada Computers. After 30 days, any GPU issues are usually handled by the manufacturer, which might not be ideal. But if you're in a location with good consumer protection laws, they might have to help you out even after that period. GPUs should last a good 5+ years, so if it breaks early, you should be compensated.