Columbia subject headings:
Canada--Commercial policy.
Free trade.
Tariff--Canada.
Tariff--United States.
United States--Commercial policy.
Harvard subject headings:
Canada--Commerce--United States.
Canada--Commercial policy.
Free trade--Canada
Free trade--United States
Free trade.
Tariff--Canada
Tariff--United States.
United States--Commerce--Canada.
United States--Commercial policy.
Princeton subject headings:
Canada--Commercial policy.
Free trade--Canada.
Free trade--United States.
Tariff--Canada.
Tariff--United States.
United States--Commercial policy.