Notwithstanding the provisions of law of the United States restricting to vessels of the United States the transportation of passengers and merchandise directly or indirectly from any port in the United States to another port of the United States, passengers may be transported on Canadian vessels between ports in southeastern Alaska, and passengers and merchandise may be transported on Canadian vessels between Hyder, Alaska, and other points in southeastern Alaska, and between Hyder, Alaska, and other points in the United States outside Alaska, either directly or via a foreign port, or for any part of the transportation until the Secretary of Transportation determines that United States-flag service is available to provide such transportation.