19 CFR 10.306 - Direct shipment to the United States.
Goods shall be considered as directly shipped to the United States from Canada for the purpose of eligibility for preferences under the Agreement only under the following circumstances:
(a) Through shipment. The goods have been shipped directly from Canada to the United States without passage through the territory of any third country; or
(b) Shipment through a third country. The goods were shipped through the territory of a third country but:
(1) The goods did not enter the commerce of any third country;
(2) The goods did not undergo any operation other than unloading, reloading, or any operation necessary to transport them to the United States or to preserve them in good condition; and
(3) All shipping and export documents show the United States as the final destination.