You don't have to have a broker to have a title search and title insurance. I think I'd first register the boat in NY - completely, then do then the documentation via the USCG, then transfer the boat to Canada - it may be anal retentive but you'll sleep better.
At a mininum I'd call a specialist in the NY area and engage them to do just that. At a guess-timate it would run you in the neighborhood of 500 or so american, and provide a priceless return on your investment. If you are taking a loan to pay for the boat your lender will insist anyway.