You need to complete and present CBSA forms B4 and B4A at the POE for any personal effects you will be bringing back with you, whether accompanied or arriving later.
Whether you need to file anything in the US depends on what you're bringing back with you and what your tax status is.
If you've been filing as a non-resident you simply file as a non-resident for 2008 and that's the end of it. If you filed as a resident (on 1040) it's very complex as you have to file a ton of paperwork to move your tax home back to Canada (but you can mail it from Canada obviously after you leave).
If you're bringing back a vehicle you acquired in the US you will need to formally import it, have a look at
www.riv.ca
There is no duty or other taxes to pay on anything imported as personal effects, including vehicles.
Steve.