ok well i've imported trucks from the us into canada twice and also helped a guy import a boat into canada. i do not know how to go the other way but each time i called the us and canadian customs offices for info and it was fairly straightforward. if the boat has a registration number and the trailer has a title, you will probably have to register the export from canada with canadian customs then take the canadian export paperwork to us customs. if not, you just pay duty if any is due. either way, start with the us customs crossing you would use to import the boat. they will tell you what you need.