At one time any manufacturer that wanted to sell goods in Canada, without punitive tariffs applied, had a Canadian subsidiary manufacturing operation, a few of which survive today, GM Canada being one of them - remember Ford Canada?  There were many others, and, if you didn't, your product wouldn't sell well here.  Many home grown Canadian manufacturers flourished in this environment - remember Electrohome?  We did just fine economically as a nation.  So go ahead, rip up NAFTA.  It would be symbolic at this point anyway.  The US can, and will, simply ignore it if they choose to do so.  Ditto for the original FTA.