Wirelessly posted (Mozilla/5.0 (Linux; Android 4.4.2; Nexus 5 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/34.0.1847.114 Mobile Safari/537.36)

Wow, this is an old thread that got bumped...

I took the Leaf recently from Toronto to NYC and at Niagara Falls, NY, we deboarded into a special room for passport checks and declaration forms (not the regular station). We were allowed to leave hand luggage on the train, but it was to have had a special transborder tag given out in Toronto. This was a different process from both the Cascades (border control in the Vancouver station) and, if I recall correctly, the Adirondack (done onboard with border agents who got on from a wayside hut).

Worth noting, in case it applies to anyone, is that Nexus cards are accepted when crossing at CBN, though you get no special priority handling. This is what you would expect since it's a WHTI-compliant land crossing document, but the Nexus paperwork doesn't say so explicitly.