I like the Wellington alignment between Yonge and University, assuming that it creates three transfer points between YUS and DRL (Union, King, and St Andrew), rather than a single point at Union.
Such alignment will distribute the transferring crowds more evenly. Moreover, many DRL passengers won't even need to transfer to YUS to get north, as they can walk to their destination (say, to King and Bay) using PATH.
East of Yonge and west of University, the line can join the rail corridor, or even venture south of it to serve places of interest such as SkyDome and Exhibition.