HOresy is right, I've looked into this stuff myself.
Autoparts that are made in the USA are not duty taxed. They will be if they aren't from the states. PST & GST will be taxed on the value in which the item is declared. Thus you shoudl ask the seller to make up a fake bill, with a lower price, and then you would have to pay the taxes on that lower bill.
if you need more information.
http://www.aacb.com/taxdutycalc.aspthat will calculate what it'll come to for you when you get to the boarder.
I woulnd't try to smuggle them, if you CAN fit the bumpers, and they for some reason pull you over. They are gonna rip apart your car, and not even put it back together.
good luck
Snafu
