Just to clarify, Canada is the largest trading partner of the US. We export a lot to the US and buy more from the US than any other country does. We buy more from the US than France, the UK, China and Japan combined.
For 37 years that trading arrangement has all been tariff free in both countries, with the exception of lumber. Other than on Lumber, and that tariff is only on the US side, neither country had protective tariffs in place. This agreement was originally called the North American Free Trade agreement. It was negotiated by Ronald Reagan and Brian Mulroney ( Canadian PM) Both leaders believed in free trade. Mexico also signed that deal.
Lumber was dealt with separately. For awhile now, the US has been adding a tariff of 14.5 % onto Canadian lumber imports. I believe the US feels that CDN stumpage rates are too low so they added a tariff. Canada never added a tariff on US lumber. Not much US lumber goes north anyhow, for a variety of reasons, mainly price but also quality.
Later on, during Trumps first term, he decided that Nafta should be renegotiated. That resulted in CUSMA, which he negotiated and signed. It is a very similar Free Trade agreement to NAFTA.
Living 1000 ft from the US Border and having Lynden, Washington as our closest town, I have made good use of both Free Trade agreements.
But yeah, it was a shock to go from zero Tariffs in both countries to this sudden 25% and then the added threat of being told by President Trump that our economy would be broken by his tariffs and that our country will be annexed by the US.
That first part is only money, not great and certainly a contravention of the signed agreement, but it's the last part that really gets folks worked up, hopefully everyone can understand why.