Canada has a dysfunctional domestic trade economy where it’s often easier to trade across borders with the U.S. than it is to trade across provinces.
Simply eliminating a lot of those domestic trade barriers would create more economic wealth than what Canada would lose by ending trade with the U.S. completely.
Of course in practice it won’t be that easy and the finances don’t usually materialize that easily, but the point is Canada has options for growth that are fully under its control.
The only sector where this is generally true is liquor. This is significant, but not massive.
Inter-provincial trade barriers for labor, especially licensed labor are also quite onerous. But it's still easier for a Quebecois tradesman to work in Ontario than it is for that same tradesman to work in the US.
Simply eliminating a lot of those domestic trade barriers would create more economic wealth than what Canada would lose by ending trade with the U.S. completely.
Of course in practice it won’t be that easy and the finances don’t usually materialize that easily, but the point is Canada has options for growth that are fully under its control.