Re: Taking non registered boat in to canada
I don't think registration in the way you mean it is going to be a problem. It's not like you are importing a purchased boat and have to prove someone transferred it legally into your name. You are coming for a visit and going home again.
That would be like the CBSA asking to see your car ownership as you cross over into Canada or USCBP asking for the same as we go from here to the US. It just isn't done unless of course they are suspicious about something.
What you will need to operate a boat in Canada over 10 hp is a boat license. Those are the numbers on either side of the bow, which I think in the US is called the registration. Registering a pleasure boat in Canada is optional (mostly). Licensing and displaying the licence numbers on a boat over the 10 hp is not.
I think you will get dinged if you are stopped in Ontario waters without (let's call them) these hull numbers. Either "foreign" numbers from registering in the US, or Canadian numbers as a result of licensing. $150-$200 I think is the fine - something in that neighbourhood.
This, of course, assumes you are boating on a lake large enough to be visited by the good folks from your nearest marine police detachment.
So, unless an eagle-eyed, boat-savvy agent notices you are over ten horsepower and have no numbers, I'd say you won't have a problem. If the engine is at the cottage already and the boat is behind your car on the trailer without one, so much the better.