How to Import a Canadian Car to the United States

Bruce's Guide to Jewish Dating

Have the title of the car signed over to your Canadian wife, who either has citizenship or a green card.
Have proof that the car was in your wife's family's posession for at least a year. This is necessary, because otherwise you will have to pay a 2.5% duty on the car.
Contact the Canadian division of the car's manufacturer, (Nissan, Toyota, etc.) and ask them for a letter saying that your car meets US emission and safety standards. They'll fax if you want.
Get temporary insurance for your car. Just call an insurer, and they'll fax you a temporary card. I think this has to be done within a short period before the next step, maybe 10 days.
Declare at Customs when you cross the border. Alternatively, you can lie at the border and say you are going for a short trip to the states, and declare it at JFK when you're ready.
Find Form MV-82 on the web and fill it out. Have your wife bring it, her license, Passport or Green Card, and Bank Statement (showing her US address) to the DMV. That will take a day. You will need to pay some fees, so find out beforehand what they are and how to pay.
Get insurance on your car and stick on the plates. And you're done!