Columbia subject headings:
Canada--Commerce--United States.
Canada--Foreign economic relations--United States.
Tariff--Canada.
Tariff--United States.
United States--Commerce--Canada.
United States--Foreign economic relations--Canada.
Harvard subject headings:
Canada--Foreign economic relations--United States.
Tariff--Canada
United States--Foreign economic relations--Canada.
Princeton subject headings:
Canada--Foreign economic relations--United States.
Tariff--Canada.
Tariff--United States.
United States--Foreign economic relations--Canada.