Think about the return trip. US customs may need proof you didn't just pick up the boat in Mexico.
I crossed at Detroit/Windsor with a canoe no questions asked by Canada and proceeded to vacation in Algonquin for 2 weeks. I returned through Sault Ste Marie where I was "detained" until a copy of the canoe's Bill of Sale could be FAXed to US Customs. That was in the late 1960s when a "FAX" meant a trip to a Western Union office.