If you ride the train one way, from Cananda to Skagway, you clear US customs at Skagway. They even have a neat steam locomotive entry stamp for your passport. I don't know where you clear customs, entering Canada, although the highway border crossing is about 50 feet from the Fraser station. Most hikers walk from the US into Canada, along the Chilcoot pass trail, and return by train, so there may not be much one way traffic into Canada. John Bush could tell us, I suppose.