For Canadians having their stuff modified in the US then returning to Canada
From:
http://www.cbsa-asfc.gc.ca/publications/pub/bsf5056-eng.htmlI'm wondering if the US has a similar policy?
Repairs or alterations to your vehicle/vessel/aircraft
If you intend to have repairs or alterations made to your vehicle/vessel/aircraft outside Canada, check with the CBSA for information before you leave. Under customs legislation, the CBSA can no longer consider your vehicle, vessel or aircraft to be Canadian-made if you increase its value, improve its condition or have it modified outside Canada. As a result, you may have to pay duty and the goods and services tax (GST) or harmonized sales tax (HST) on the entire value of the vehicle/vessel/aircraft when you bring it back.
No duty will apply to the value of the repairs or alterations made to your vehicle/vessel/aircraft in the United States, Mexico, Chile, Costa Rica, Israel or another Canada-Israel Free Trade Agreement beneficiary when it is re-imported into Canada; however, the GST/HST will apply.
Emergency repairs can be made to your vehicle/vessel/aircraft while you are travelling outside the country to ensure your safe return to Canada. However, to be eligible for this special provision, be sure to declare the value of all repairs and replacement parts when you return to Canada with the vehicle.