I just don't see a political alternative to building the Scarborough Subway. There were quiet grumblings when David Miller brought in Transit City and the continuation of the segregated SRT with transfer. When Ford was elected, people just wanted Scarborough connected and the combined SRT/ECLRT was born. Within a year, this was killed in an effort to stop Ford. Realizing what a mess they made, both the Provincial Liberals and City Council has for 5 years now been telling the public that Scarborough deserves a subway and nothing but a tunneled subway will do.
It just seems too risky for any party to campaign against the subway. If you go back to Transit City, the same segregated Scaroborough arguments will be made. If you propose something else (cut-and-cover subway, Smart Spur - a branch of the SmartTrack, or a whole new line from Malvern to Centennial to STC to Don Valley to Downtown), the public will view it as not equivalent to the subway that is currently on the table, and also as an attempt to defer construction of anything for Scarborough. The only chance is for a political party to lie or deceive during the election campaign (say your in favour of the Scarborough Subway with some caveat), and then shorten planning, and begin construction, and be well through construction, before the subsequent election. The only thing that can be built this fast is an elevated line.