Here’s the Canadian prime minister talking about Canada’s steel trade with the US;
http://www.freerepublic.com/focus/f-news/3636689/posts
Canada is the #1 importer of steel to the US. They are a conduit not a manufacturer.
Based on USTR numbers, I suspect Canada does make a lot of steel. Its Chinese imports amounted to about 600m tons. That would be a lot more if it were mainly a conduit.
https://www.trade.gov/steel/countries/pdfs/imports-Canada.pdf
I think the real problem with Chinese dumping is similar to an oil glut. There’s basically one global price for a given commodity, adjusted for grades and transportation costs. Global arbitrage means if China’s price is the cheapest, everyone demands the Chinese price. That’s not good for bottom lines if Chinese steel manufacturers are getting interest-free loans that never have to be paid back.