More Americans working plus non income tax revenue. A win-win.
Where is the incentive to do that? Canadian lumber is taxed, not cut off. The lumber industry was selling all the could produce before. Now they're selling all they can produce except for 20% more. Increasing their own production will drive prices down and cut their profits.
There's some dispute about whether Canada is really "dumping" lumber in the U.S. at all, but two things I know for sure:
1. The U.S. consistently loses to Canada when this issue is subject to rulings by international trade boards.
2. It's no coincidence that lumber imports from Canada grow considerably when the Canadian dollar weakens against the U.S. dollar.