The bridges at Cornwall were removed by the St. Lawrence Seaway, the south span in 1958 and the north span in 1965. Meanwhile, Canadian National Railways purchased the Canadian portion of the route in April 1957 and used the rails to build a new hump yard in Montreal. They left a section from Hawthorne to the Terminal Avenue Yard in Ottawa, and then by the end of 1957 reopened a portion from Hawthorne to Ramsayville. This relaid section was removed in 1972. The remaining track in Ottawa was in service until 2002 when the Ottawa Central Railway removed the tracks opposite the Canada Science and Technology Museum to the yard. On November 1, 2008 the Ottawa Central was purchased by Canadian National Railway. In Cornwall, the track was relaid from the Canadian National Railway main line to what was once Cornwall Junctionin 1971 as the Wesco Spur.
In the United States, the track from Rooseveltown to Helena has remained in use since the New York Central Railroad years. It has managed to survive Penn Central Transportation, Conrail, and CSX ownership and is still in use presently. The track in Tupper Lake was used until Penn Central abandoned it in 1972, but was put back in service by the Adirondack Railway from 1979 to 1981. Today, the tracks remain on the right-of-way for future use by the Adirondack Scenic Railroad. They have been pulled up at the road crossings, but the connection to the Adirondack Branch is still in place.
When one mentions the New York Central you immediately think Grand Central, Hudson's, Niagara's, 20th Century Ltd, 4 Track Mainlines and so on.
However, it really was a small time, rural, Hooterville operation in all the states and provinces it served. I suppose all those little veinlets fed into the secondaries and into the mains. Almost all of them had small time but vital passenger service that lasted a very long time, with the last of them extinct by 1960.
I'm willing to wager that the Ottawa Division played a bigger and important role in WWII that few know about.