My boyfriend is Canadian. When he got a TN for his most recent job, he applied for the TN on the trip that he was apartment hunting, so that was done at the airport. He then entered with all his stuff, I think about a month later, by car.

And then when he was going from TN to Green Card, we specifically drove across the Peace Bridge and back, just so he could reenter and get a new TN (making sure his TN wouldn't expire during the green card application process). That's always fun, because even though we both have NEXUS, they always look at us funny since I'm USA and he is Canadian.

Remember too, you will enter the USA and apply for the TN, but when you return to Canada, they don't care if you have a TN or not, as now you are entering as a Canadian citizen. If they ask the purpose of your short trip to the USA, you can just say you were getting your visa taken care of.

As for duties, I don't know. My by didn't move that much stuff, but he did have to import the car. Importing a car into the USA didn't seem to be a big deal.

And, of course, I am not a lawyer.