19 CFR § 123.28 - Merchandise remaining in or exported to Canada or Mexico.
(a) In-transit status abandoned. When the in-transit status of merchandise transiting Canada or Mexico is abandoned and the merchandise is entered for consumption or other disposition in Canada or Mexico, the carrier must send the in-transit seals and manifests to the port where the manifests were first filed with CBP, or in the case of trucks under subpart E, the port of exit, with an endorsement by the carrier's agent on each manifest showing that the merchandise was so entered. The carriers must comply with the export control regulations, 15 CFR part 370.
(b) In-transit merchandise exported to Canada or Mexico. Merchandise to be exported to Canada or Mexico after moving in-transit through a contiguous country will be treated as ex ported when it has passed through the last port of exit from the United States. This paragraph will control whether or not the merchandise to be exported is domestic or foreign and whether or not it is exported with benefit of drawback. The manifest, Electronic Export Information (EEI) filing citations, exclusions, and/or exemption legends, and the notice of exportation, if any, must be filed at the last port of exit from the United States.