Posted: Mon Sep 15, 2008 9:17 pm-
As a visitor you can keep a Canadian-plated vehicle for a year, but you're not a visitor so you would have to formally import it immediately. Can't see why you would want to keep Canadian plates on it if you live in the US. There's no duty because it's a personal effect.
Declare it to CBP and get a conditional clearance, get the EPA check done any State required checks and take the paperwork to the local CBP office and get the clearance completed and then you can swap the title for a US one and get the car registered.
Most Canadian insurance companies will cover you for up to a year in the US so it shouldn't be a major problem, read this also as it contains more details:
http://www.cbp.gov/xp/cgov/trade/basic_trade/importing_car.xml
For some reason it's vague about the duty-free bit, that's contained in the CBP guidance on personal effects.
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Steve.