The American tariff will only hurt the American consumer, who will now pay inflated prices for lumber. True, 75% of our lumber exports go to the USA, and it will hurt firms in the short term, but perhaps this is a perfect opportunity to find ways of selling to other customers. For too long we have been dependent on the monster south of the border. It should now be a National priority to develop alternative markets for all our exports. First step should be developing and modernizing all our sea ports. 
Although the temptation is to retaliate with tariffs of our own, all that does is make everything more expensive for us. 
Trudeau started his term by backing down from Obama's snub to the Keystone pipeline. A "fresh start", he called it. Wonder how he'll handle this one.