There are confidential commercial discussions going on with CN, and I've signed a non-disclosure agreement with them not to say too much, but I can give you a general view.
Today, CN goes from Bramalea up to Georgetown, then south. That's their main line to serve both Buffalo and Sarnia. This proposed route is about seven miles shorter, and for CN there's some commercial strategy upside to that. For GO Transit there's an upside, because that frees up the capacity that CN would otherwise use on their current corridor for future GO traffic, to increase the movement between Union Station all the way to Kitchener.
So that's what's in it for both parties. The discussion with CP continues. There's a remote possibility of some co-sharing on the so-called Missing Link, but I think the more viable option would be expansion of their current Milton corridor.