What rules for Canadian pickup towing utility trailer in US?

Some states automatically put a commercial license plate on over certain weights, a 1 ton pickup is a frequent example. That doesn't mean you are commercial. Driving a personal vehicle pulling a personal trailer not for hire, I would never consider stopping at the scales. They don't want private vehicles clogging up the commercial truck lines.

Wadcutter is the expert, no doubt about that. Pay attention to what he said.