The only way the Canadians can reduce their unit costs is to increase production, which would lower the market price. There's no reason to do that, since, before the tariffs, they were already out-pricing the US (selling below cost? maybe just to keep US competition at bay) and probably making their money in other markets.
Now that the tariffs are in place, they increase production, flooding the market, because they'd rather see the glut eventually bring the price lower than pay extra duties to the US.
Hmm... dunno if that makes sense.
Not buying it.