I think you will find you can drive any vehicle up to 26000# with your regular driving licence. But only for 90 days.
After that you need a Canadian licence, which would need a Canadian address.
Insurance in Canada is not cheap. It would cover driving in America, but would also need a Canadian address as a base.
Road fund tax as you call it is a sticker on the vehicle license plate, good for one year. A LOT cheaper than the UK.
Buying a unit in Canada and travelling as you propose should not be a big deal..............
BUT selling a Canadian unit in the US will be a HUGE issue. You would be importing the unit which must meet all US Safety and Emission standards and must have a letter from the Manufacturer to that effect AND stating all recalls have been done.
Good luck with that!
Vehicles in Canada are significantly more expensive than in America, so, even if you got the legalities taken care of, you will lose your shirt on that sale anyway!
