Instead of worrying about domestic production, how about entangling the two economies such that they can't afford to attack each other. Canada, USA, and Mexcio aren't going to start shooting at each other because any attack would ruin the attacker's supply chain -- and customer base.

This is similar to the NATO principle: entangle the countries' military objectives together but don't make it worthwhile for them to invest in actual military power -- essentials bribing them to not be able fight wars (this is why complaining that they don't pay "enough" is potentially destabilizing and could cost more later).