If this proposal becomes reality how could this effect New England railroads?
I don't know specific situations but in general:
Tariffs raise the price of imported goods. If the price of Canadian lumber becomes higher than other lumber in the market, buyers will go elsewhere for supply. If the new source for lumber is ME, VT or NH, then they may not lose (but probably do to trucks). If it is OR, WA or MN, ND or the like, then they lose.