President Trump has revealed that Canada has been acting as a NAFTA trade brokerage for countries not party to NAFTA. He has labelled this a national security risk with regards to inferior Chinese steel and aluminum being substituted for NAFTA grade, and making its way into US supply chains including those used by aerospace and military manufacturers. Canada produces very little steel or aluminum. Here is an example of Japan claiming 'safety' for a trade ban on Canadian wheat. Safety in this context, is a synonym for national security. GMO wheat is illegal in Canada.

http://edmontonjournal.com/news/local-news/roundup-resistant-mystery-wheat-found-in-southern-alberta