Duties on Canadian imports are driving up domestic sales at some Maine lumber companies. …Protection from historically lower Canadian lumber prices has given Pleasant River Lumber the confidence to add an additional manufacturing shift in Enfield, according to co-owner Jason Brochu. Photo by Katherine Emery. …Historically Canadian companies have both outbid them for timber harvested in Maine and undercut American lumber prices when they export the finished lumber product back across the border. …An industry analyst and two other mill leaders said that inflation and a sputtering housing market make it unclear whether the tariffs will have a positive or negative effect on business in the long run. The effects of the tariffs will also vary based on the different products sawmills make. …Sawmills rely on certainty, said Alden Robbins, of Robbins Lumber, and neither the markets nor foreign trade relationships have been stable recently.