The sale of the Massena Line to Canadian National is clearly connected to the joint CSX-CN intermodal services that were announced a few weeks ago. CN buying the line means that they are going to get a greater share of the line haul for this traffic then they otherwise would have gotten. CN also wants to grow their traffic, especially in Eastern Canada, where their mainline is underused. By acquiring the Massena Line, it gives CN more control over what traffic from the Eastern US is put on it's rails in Eastern Canada.
The sale only goes as far south as Woodard, New York so that CSX can still access their Oswego Line without the use of trackage rights, and to retain the industry directly north of Syracuse. The deal is almost certin to include trackge rights to the CSX yard in East Syracuse, but doesn't include any way to directly interchange with the NYS&W. This is done so that CSX can solely decide what is put on and off CN at Syracuse.
It is possible that in the upcoming STB review, that the Susie-Q can force in a provision that allows it to interchange with CN, but I don't see that as likely, considering that CSX owns 40% of the stock in the NYS&W.
C&O: George Washington's Railroad!