Bringing in less lumber also reduces dock jobs.
As the price of lumber goes up, there are more European imports coming into the east coast ports(Baltimore, Charleston, Savannah, New Orleans and Houston). My company brings containers of lumber from Europe into all of these ports. other companies bring in Radiata Pine from Brazil, Chile and New Zealand.
I can not think of any lumber from Canada that is brought into the US on a ship. It is all shipped via railcar, flatbed truck and enclosed vans.
It is more a function of the exchange rate between the US dollar and the foreign currency.
Lumber, and most trade, between Canada an the US is by truck or train. No dock workers are harmed.