I've brought in lots of auto parts from the US, and I would never use UPS across the border. They tack on so many fees its crazy, plus they have never got a duty classification right yet for me. Why should I pay $50 for the priviledge of them screwing it up?
If I have to have it overnight, its Fedex, otherwise the Postoffice. The postoffice usually takes about the same time as a ground courier, and the fees are much less.