I have bought 6 sets of wheels/tires from Discount Tire Direct and they are great to deal with. Once they had actually installed one of the tires backwards on the wheel (directional tire), I just called them and told them what happened and they said no problem, take it to any shop and have them switch it around and call them back and let them know how much it was. I did that and they refunded that amount x2 for the hassle.
I always have my things from the States shipped to USAddress Inc. in Niagara Falls NY. I can get there in about 25 minutes from home, and is roughly half the distance as Buffalo. Plus then you can grab something to eat at the Brickyard in Lewiston

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One thing... DO NOT try to evade duty charges by installing the new wheels/tires across the border and not claiming them. They know what your car looked like going over and its not hard to tell if you are rocking brand new wheels/tires on the way back. Not saying that you would think to try this, but just in case you did, don't lol.