In a trade war with Canada most US industries would suffer most

Donald Trump's announcement today that the US plans to impose huge tariffs on steel and aluminum imports threatens to spark a trade war with one of the US's closest allies, Canada. 

Canada is the top exporter of both steel and aluminum to the US. It manufactures 17% of all of US steel imports and 43% of all aluminum imports. "Should restrictions be imposed on Canadian steel and aluminum products, Canada will take responsive measures to defend its trade interests and workers," Canadian foreign minster Chrystia Freeland said soon after the Trump announcement.

Canada would have plenty of ammunition; it is the largest market for US goods, and purchased some $266 billion worth in 2016. In 2016, the US ran a trade surplus of $12.5 billion with Canada, when both goods and services are taken into account. If Canada retaliates by slapping import tariffs of its own on US goods, automakers, farmers, and manufacturers of machinery like semiconductors and electric motors will suffer.

These US industries exported most to Canada in 2016, according to US government trade data: