Why Would a New Limit on Trade in Goods with Canada

Why would a new limit on trade in goods with Canada by the United States be more important to the Canadian economy than the same type of policy in Italy?

A) The United States and Canada have the same political system.
B) The United States ranks behind only the United Kingdom as our second most important trade partner.
C) The United States is Canada's largest trading partner.
D) The American and Canadian cultures are very similar, so Canadian citizens are more likely to want the same types of goods and services as the Americans have.