Can cars drive on the Ground level of Pearson Terminal 1 in Toronto Ontario or is that level only for buses, taxis, and airport shuttles?
Pearson Terminal 1, like all the terminals, has places where individuals can drop or pick up other people. They are the same places where taxis and busses drop and pick up people, right outside the departures/arrivals entrance.
If you are dropping, you can simply drive to the 'departures' area, stop briefly, let the person out and drive away. You will be right there with the taxis and limos.
If you are picking up, the only complication is that you are not allowed to wait in that area. What most private individuals do is to park in the short term parking (which of course costs money) and walk to arrivals, where you pick up your friend and walk back to the car. Alternatively you can wait in the free cell phone parking lot (thanks Michael Hampton), have them call you when they are completely ready to be picked up, arrange an exact point to meet at arrivals, and then drive in to pick them up while they wait. If you need to do this because the person you are picking up has difficulty walking, check to see if the airport will provide special services for them.