The original Transit Hub concept is dead. It was modeled after Schiphol: a cluster of Office buildings intended to supplement Pearson's income to reduce fees on airlines and passengers. This is why airlines bought into it so readily; they weren't expected to pay for the project and would get relief on landing fees.
If airlines are expected to foot the bill through fees, I'd wager Woodbine GO will be the north-west Transit hub [especially if Woodbine Racetrack kicks in for station upgrades for LRT connections] and it will be connected through an upgrade of the existing people mover. The PM tech can run multiple trains per track, at 3 minute frequencies, and much longer distances by changing some of the hardware.