forms for bringing parts across the border

Per my experience with Canada Customs:

(1) Normally Canada Customs won't bother you with used auto parts.

(2) New auto parts may require a visit to the secondary checkpoint. It depends on the customs agent you are dealing with. You will be given a form to fill out and you may be hit with duties and taxes.

(2b) Any new parts ordered from a US company will come with the carrier's customs papers. You pay the carrier duty/taxes/delivery charges.

(3) Vehicles must be 15 years old to avoid any duties. Taxes are assessed on Blue Book value or your receipt, which ever is the greatest. A/C taxes will apply to all vehicles. You will be given a form to fill out for plateable vehicles.

(3b) If you're bringing back a "potential race car" it will depend on the agent you get. I've brought back two rolling shells in the past 5 years and didn't pay any duties or taxes.

If you need more detail google Canada Customs - Importing Goods Guiedlines.

One suggestion; be honest with the Canada Customs people. If you try to pull one over on them and get caught, you will pay!!!