If one is planning to move from Canada to the US for a long period of time, what documentation is required at the border to import one's personal items? Does it matter if you drive a UHaul truck with your personal belongings rather than taking a regular car?
According to US Customs and Border Protection (CBP), you need to fill out form 6059B which is available here. It's a fillable PDF form Note: I couldn't open the form with my version of Acrobat Reader but I don't have the latest version.
Elsewhere, it says that you must have complete lists of both household effects like furniture, artwork, dishes, etc. and personal effects like clothes, photographs, electronics, and so on. Just listing "household good" or similar is not sufficient.
Your goods should also have been in your possession for a year at least. Buying new goods and immediately importing could cause duty to be assessed.