de-icing seems to be on an airport by airport basis.

In YYZ, there's a central pad (with multiple stations), and it seems that they sequence the planes through in their 'launch' order so they'll deice one, and then it can get in the takeoff queue with sufficient glycol time left.

In LGA it seems to be done at the gate.

In CLE there's a central pad... (also, in CLE they had a infra-red deicer for a while, don't know what happened with that, was supposed to be a nice innovation..)