If steel and aluminum is imported to Canada, they face Canadian tariff rates. If the US and Canada coordinate their tariff regimes (as I illustrated with the EV example), the rolled steel and aluminum will be tariffed at a rate the US government deems adequate.

If you're suggesting that Canada is facilitating the covert smuggling of Chinese steel and aluminum then I'd require a bit more evidence. It's become fashionable for the US government to level such accusations, but as we saw with claims about fentanyl, it's all bunk.