First of all, Canada needs to keep that arrangement as constrained as possible. Treat it as an experiment that needs to be ring-fenced from the rest of the economy and industry. See how it goes. Make sure it is reversible if it begins to have obvious negative effects, which, frankly, I think it's likely to. I don't think this strategy has the potential to drive investment or much technological innovation in the sector because it will deter companies in other countries from entering.
Most likely, what we're going to see with Chinese EV companies is them setting up knock-down kits, where all they're really doing is circumventing trade barriers. Unless you have an integrated North American market, I doubt very much that they're going to be seriously interested in building proper, full plants that would sustain a technological ecosystem and help us build that whole supply chain locally. The Chinese government is on record as wanting to restrict its EV companies from transferring technology and process knowledge. If you look at the limited examples in Europe or other...it's usually knock-down kit plants, or they are importing their own workers and not transferring any technology.
I don't see how Canada is going to have the leverage to do that. The only scenario where that might be possible is if you have an integrated North American market under CUSMA, in which the U.S., Canada and Mexico all impose the same standards and are then able to use that massive leverage to potentially oblige Chinese companies to come in and actually contribute in a way that is positive but carefully restricted and managed. Alone, I don't see how Canada can do that.