It's important to remember that if the costs of compliance in a revised NAFTA become too high, the external duty rate the U.S. applies to cars is 2.5%, so a cost increase beyond 2.5% might very well lead some manufacturers to decide to relocate manufacturing out of the region. There is a real downside to disrupting those supply chains.
Evidence of meeting #71 for International Trade in the 42nd Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was vehicles.
A video is available from Parliament.