At the moment I can't for the life of me think of what CBN actually means, but it's got something to do with the Canadian Border. When that train crosses the border into Canada it stops running with Amtrak crews and starts running with a crew from VIA Rail, Canada's version of Amtrak. The train even gets a new train number when it crosses the border.
You however don't even have to move out of your seat. They do customs right on board the train, the new crew boards the train, and off you go in the very same car.
You will also get two tickets, one to hand to the Amtrak crew, one to hand to the VIA Rail crew.