Why not just drive down to Minnesota or Michigan? and save a couple of pennies?
When you factor in the exchange rate and the hassles to get it back over the border then it's not worth it. I also register my bikes so that I can drive them on trails and you can't plate a motocross bike purchased from the states in Canada. If your only going to ride them on private property then you don't have to worry about registration and paying sales tax but in my case I do.
I also have a good dealer that I like to stay loyal to. It's important when purchasing a bike with little to no warranty. Anyway back to the new Yz450 discussions ;-)