The ultimate goal is to get all the auto manufacturers to move their production out of Ontario to the USA instead. Which probably isn't terribly realistic as manufacturers know that governments change, and today's billion dollar decisions to open/close a manufacturing facility may turn out to be a billion dollar mistake a few years down the road.
In normal times, anyways. We're definitely in abnormal times.
In the end the automakers might just move to Mexico instead, but then of course Trump would just kneekerk into tarrifing them instead. Again, the goal is to get automakers to move their plants to the USA.
But the supply chain would still grind automakers to a halt inside a week or two if this happens as there's just too many parts made in too many countries for that to happen overnight. It would take probably 6-12 months to suddenly yank manufacturing contracts from factories in Canada and Mexico and move them all to the USA. During that time, the cost of their product shoots up insanely, sales crater, and consumers will lose their minds.
None of this goes beyond simplistic desires of a crazy person without any consideration to reality.