I know the idea of a subway line under Queen has a long history to it and a lot of folks think it's the obvious choice, but I think it's a bad one. Building it would cause transit chaos downtown for years. Queen already has a transit line that can handle all of its own demand. It is lined with heritage buildings that, let's face it, would "accidentally" burn down and be replaced by 40-story cookie-cutter boxes about 20 minutes after the subway opened.
The Front corridor is in the process of being built up with much greater heights and densities than Queen, and is poorly served by transit. It has important regional destinations like the Dome, the convention centre, and the Exhibition that would benefit from a subway line. Building it would not involve scrapping an existing transit investment and would be less disruptive in terms of transit, people's lives, and heritage.