I have brought many carloads of boat stuff into Canada on both coasts, probably 50 times over 12 years. I've experimented a bit with what to say. You must remember that customs officials - even Canadian ones - have no sense of humor. Never lie, but never offer more information than is absolutely necessary.
My conclusion is to say "I have only personal stuff, all of it is leaving with me". If they decide to do a strip search you haven't lied. It does not light up any suspicions needing to be explored further. A couple of times I tried "just some parts to install on my boat" and this led to 1/2 hour or more in the office with lengthy explanations, resulting in being allowed through with no taxes or duty. But a goodly delay.
Twice I've come in with the car/truck piled to the roof with stuff. Hard to ignore. Last week was the latest. They tossed the truck completely while I waited in the office, then handed me my keys and passport and said "have a nice day".