I typically order all my athletic clothing and shoes from: www.eastbay.com
The site has a 25% off sale that ends today for memorial day weekend. The price savings vs Canada can be quite good, for example:

Kobe V basketball shoes
Footlocker Canada: $199
EastBay: $129
EastBay 25% off: $97

Nike Free Run running shoes
Footlocker: $119
EastBay: $84
EastBay 25% off: $63

The best deal I found was Footlocker buy one, get one 1/2 off. For the 2 above shoes:
Footlocker 2-for-1: $260
EastBay 25%: $160

I spent the $100 on new motorcycle gloves instead

Shipping was $10 to Point Roberts, and the ~50% savings translates to ~50% saved on tax which more than pays the duty.

If you don't know your size, go into Footlocker or SportChek and try them on. I was actually told about EastBay by a SportChek employee who said the prices even beat his employee discount.