Well!, one way for CP to get on to CN Halton Sub and will piss the residents off in Weston is to do a connection where CP crosses CN line east of the Humber River. This means the traffic on the MacTire Sub will double to triple the current amount of trains on line.
I have no idea if this is grade separated or not since I have never been there and if so, who pass over the other? CP will have to double track the MacTire Sub to allow for the increase traffic on the line south of the Halton Sub with triple track to allow trains on/off the Halton sub new 4 track corridor.
CP will have to double track the connection to North Toronto Sub to allow trains pass each other without having to deal with stop and go.
At the same time, a new interchange yard can be built on the Halton Sub to allow faster and shorter hand off between both system. This will mean the end of Lambton Yard 100%, freeing up land for redevelopment, as well a new GO Station to service both the Milton Line and the Crosstown Line. The new interchange yard could be in the middle of both lines with CP being on the south side.
If this is a no go, ML better get off their ass and 4 track the Galt Sub as per Wynne 2014 election platform. Otherwise, still talking about this 20 years from now and riders getting the shaft like they have since 2011 fail triple track program.