Since when does the US west coast depend on Canadian hydro electric generation? WA state has so much hydro the price goes negative every spring when the snow melts. There’s a half dozen LNG generators state wide for supply stabilization, several wind farms and solar arrays.
And the line loss would be too great to economically ship canadian electricity to California
Being able to import a few percent when you need it and export a few when you don't without having to spin something down is pretty important to having a stable power grid.
The reality is that there is no dividing line between Canada and U.S. when it comes to electricity. Power grids cross the 49th at will. In California, you're on the same interconnection as Vancouver and Calgary.
Conflict would disrupt power in both countries, and much further from the border than you may suspect.
And the line loss would be too great to economically ship canadian electricity to California