If he has his way, Trump will kill Canada's automotive industry. If you accept this as forgone, maybe partnering with the Chinese to create a new auto industry is a good idea.
Just because the companies building cars in Canada are headquartered in the USA doesn't mean Canada doesn't have an automotive industry. The factories, equipment, and workers are on Canadian soil could always be nationalized (not without retaliation of course).
Yes, the Canadian auto industry will take a hit, but it already has from the US (and might take more).