Think about that for a moment.
I think it's safe to assume that any agreement in which Canada stipulated that Chinese EVs can/must be sold in the Canadian market would include needing to meet regulatory requirements both Canada and the US have. (The dip in cross border travel notwithstanding, a car you cannot drive in the US from Canada would be orders of magnitude harder to sell to Canadian consumers.)
I imagine China would not have a problem with this, for what should be fairly obvious reasons. Selling cars to Canadians would represent an excellent opportunity to expose American consumers to Chinese EV vehicles on the ground via visiting Canadians. That's a kind of exposure they have not been able to have with the current USA/Canadian market barriers.
China produces vehicles for a ton of markets. Meeting the regulations of those markets is not something new to them.