This Timmy's is located on the arrivals level (gates) in the domestic section in Terminal 3 post security.
After the post security of the B and C gates of Terminal 3 and just to the left there's a Timmy's that seems to be more organized than the Tim's in Terminal 1. I admin I rarely go to Terminal 3 as opposed to 1 so I can't ever say I remember coming to this particular Tim's before. The one thing you'll notice that it's quite busy with 3 separate lines going but no lines in particular for just beverages so all three are full service (food and all).
The pickups seem to all take place at the right side and that area can get a bit uncomfortably packed if many are waiting for their orders. They're calling our orders by number for pickup so try to remember your number or check your receipt for the last 2 digits.
As always I'm no fan of Tim's breakfast sandwiches. Everything just tastes reheated and doesn't seem as fresh as A&W or McD's for quick breakfasts. Their coffee is ok.
They don't seem to have their own seating so if you head down to where the other places are (the area that looks like a food court) there may be seating there. It seems the gates at Term 3 don't have side tables in the seating area like they do in T1 so eating there will be more difficult with no place to really down your drink except for the floor if you have to resort to that.