from America first to full on protectionism. I don't think this is gonna pan out well trump.
Protectionism will only hurt both sides.
Canada should have a very firm and direct response. Tear up NAFTA, walk away from further negotiations and impose a 220% tariff on all US goods entering the country.
Any trade war will hurt both sides no doubt. First, we should try to avoid a trade war and de-escalate.
Second, if that's not possible, and recognizing that any trade war will inevitably hurt both sides, then let's at least try to ensure maximum pain to the US and minimum for Canada to the degree possible.
For that, I'd propose a per-weight and per-kw export tax. This would contribute to a reverse-Dutch-disease effect by reducing Canadian raw-materials exports to the US, lower the Canadian dollar, and so increase Canadian manufacturing exports to the US.