Not hard
Just did this in November.
I rented a Ryder truck in CT where I live. Be sure to tell them you're going to Canada, slightly different insurance. I called Customs at my intended crossing, but in the end used FedEx customs brokerage to get paperwork right; cost about $180. Understand that both countries are nervous about lone men driving rental trucks across the border, so you need to document the vehicle and all people who will go into Canada as well as the vehicle, driver and passengers AND the contents coming back into the U.S. The peace of mind knowing that everything was correct and already in the hands of the Customs Inspectirs when you drove up was priceless.
Yes, you're bringing "airplane parts", but I went with "partially completed, never finished, never flown aircraft kit" also, remember, the kit originated in the US, you're not importing a Canadian product.
Just have copies of everything: Bill of sale, your passport, insurance on truck, all customs documents and it was easy. The actual crossing into the U.S. was funny: they made me open up the truck, but really they were just curious! "So, is this a prop plant?" "Yes" "Is it for one or two people?" "two, hey you just want to jump up there and take a look?" "No, we're fine, but where does the wing go?"
Just like building the plane: it's all in the prep work.