[Canuck]

I have not done a trade, shipping your car into the US is no big deal, the buyer will be responsible for registration in his/her state and deal with their own tax situation.If the tranaction took place on Canadian soil you might stand a chance of it being considered a trade.
I am guessing here but I feel pretty sure Canada Revenue agency will want their GST on the full value of what the car your purchasing. As the transactions will not be simultanious. Best call a custome broker and see if they can shed some light