If it's a North American built boat there will be no duty, but there would be taxes. If it's euro or Asian built then duty would apply. BUT... none of that should matter until you actually import the boat, so I guess it's going to come down to the definition of 'importing' (I'd hope that involved actually registering or licensing the boat, as opposed to 'passing through')
With your dual citizenship you can be an 'American' passing through Canadian waters, n'est pas?
Ask Jackdale to help you sail it from WA to Alaska around the outside!!