Decent brunch near airport for 11ish on a Saturday? Is that remotely possible?
If you like dim sum, I'd go with the Grand.
I haven't been to that particular Milestone's in a couple years, but the 2 meals I've ordered at that Milestone's weren't nearly as good as the generally mediocre-to-decent food I've been served at the other half dozen Milestone's I've visited. Hopefully they've improved their game.
There's also a 24 h Perkins that serves breakfast/ brunch near the airport.
646 Dixon Rd, Toronto, ON M9W1J1, CA
Perkins Family Restaurant
600 Dixon Rd, Toronto, ON M9W1J1, CA
If you want greasy spoon, then Zet's would be the place. It's been years since I've been, but the hotel attached to LBPIA used to have one of the best AYCE brunches I've had in T.O. But it is the airport, so there's a bit of a price gouge, especially once you factor in parking.