If the US goal is 85% North American content on autos sold in North America and the distribution of that 85% is 50%US, 25%Canada, 25% Mexico that would/should/could be an acceptable future state for the North American Market.  The rules that this distribution of market follows could/should be the current NAFTA regulatory system.  

Perhaps the same could apply to goods and services, and infrastructure (Federal, Municipal, State and Provincial).   

But that might be too straight forward and contrary to the objective of employ lawyers, economists, and accountants to be subjected to the tax payer paid dry washing of hands by special interests.  

Goodness knows we don't want to have anyone actually provide goods or services before the pie has been divided.