As part of his executive action announcing the new tariffs, Trump issued three proclamations.

These list US complaints over trade issues that were previously known to Canada - signalling a breakdown of trade negotiations between the two neighbours. They relate to cars, dairy products and alcohol.

On cars, Trump's proclamation pointed to Canada charging a tax on imports of US motor vehicles and parts that are not covered under USMCA.

He argues it is "unreasonable" and that Canada has discriminated against the US by not charging other countries a similar tax.

Automotive manufacturing in North America is highly integrated between Canada, the US and Mexico.

Dairy, meanwhile, has long been a problem for the US, specifically Canada's supply management system, which sets limits on foreign imports. Those that exceed the limit are charged a tariff up to 300%.

And lastly, the enduring boycott of US alcoholic drinks by most Canadian provinces has become a major sore point for the Americans since it was imposed last year.

Canadian premiers have said repeatedly that the boycott will be lifted if the US removes its tariffs on key Canadian sectors, including metals and automobiles.

Canadian trade negotiators have been trying to secure a deal that would at least reduce some of the current US tariffs.

Read More