I decided on the ALT Hotel at Toronto Pearson airport, based on reports on Plane Spotting Hotels. They recommended rooms 1010, 1110, 1210 or 1310. A quick e-mail to the hotel secured room 1201, which has great views across the airport. Note it only has one bed (not a problem for me as I was travelling solo). It is reached by the airport shuttle train and well sign-posted. From the room you get views of the terminal ramps, although some things are hidden, as well as across to the Westjet / Porter hangars and Skyservice FBO. The 737 and E170 on the fire dump can also be seen. Good optics will allow a lot to be read off, although most on the FBO are nose/tail on. There are distant views of the Bombardier production facility, although the flight test ramp is hidden. There do not appear to be any shops / eateries in easy walking distance, but you can always hop on the airport transit train and get something in the terminal. There is a restaurant / bar at the hotel, but not the cheapest.
Location: https://maps.app.goo.gl/HFtnHCuZNwibinZY7
Credit Steve Mitchell