In the end, what's more valuable:

1) point-to-point GX pax opriginating or terminating in YYZ; or

2) US -> International pax connecting through YYZ?

With all due respect to my learned friends on the board from such points far flung as YXU and YGK, I think the answer is 2). AC (and previously CP) both did very well with sterile transit in YVR, a similar facility in YYZ would prove to be very lucrative.