I think you may have some trouble coz CAD customs will need ur registration and title for importation.
Besides, you need to inform the US customs 72 hrs before you arrive for exportation. and you need to fax them the registration and title too.
I hope you have them already. if you bought with financing, you may not able to export the car.
Here is the link about the documents you need. it is not the official website but quite acurate:
http://modena.intergate.ca/personal/rajanr/Van_File/B4_Arriv.html
The official site(canadian) is here: http://www.riv.ca/english/html/about_riv.html
The import duty for cars from US is free, but there is a fee about CAD$180. But i am not sure if that applies to new cars..... Good luck