For what it's worth, chatting with the Lake Champlain Ferry fare collector on the Port Kent side in 2014 or 2015, CN runs 4 freights a day on the Rouses Point sub, one each way to and from Vermont and NY. I have my doubts about the NY ones. But that does not merit 79 MPH operation from their standpoint, not like the Vermont route is theirs anymore as it was the Central Vermont Rwy.
The Montrealer and Adirondack routes are identical from Cantic-north. But CN is making infrastucture demands on the portion unique to the Montrealer: automating the Auburg trestle movement and remote control of the switch at Cantic. It is hand thrown, normally set for the visually diverging route to Vermont.
As I was told by the Essex Jct station caretaker, who knows lots of people on the CN, and had a long career with the CV, Vermonter crews would have to learn CN operating rules, some Canadian railroad regs, qualify for the route, and learn French. He hoped CN labor unions don't make a fuss about operating the train themselves north of St Albans due to historical precedent. That made the train's operation of three 5-person crews (one north in the AM, one to the VIA Rail yard, one south in the PM) ridiculously expensive for the 72 miles, and prompted Tom Downs to kill the Montrealer.