The more relevant info you provide the more relevant responses can be. Now you have added Mississauga is your destination for a couple of trips. But Mississauga is a large area still and some places far more accessible than others. If where you plan to visit for example is steps away from a Go Station, the answer will differ from a house in the middle of suburbia that you can't get close to by public transportation at all.
Coming from the airport to your hotel, it is easy to take the express train to Union Station and from there it is a not unreasonable stroll even wheeling a suitcase, to your hotel. That's probably the simplest and most cost effective way to get to the hotel. For your visits to Mississauga however you have to weigh cost, convenience, hassle, etc. of the various ways to do it depending on your actual destination's location in Mississauga.
So from airport:
https://www.torontopearson.com/en/toandfrom/upexpress/#
From Union Station to your hotel walking:
From hotel to Mississauga, walk to Union Station and then take Go to nearest point in Mississauga:
https://www.gotransit.com/en/trip-pl...-and-route-map
Then Uber or taxi if not walkable to your final destination.
If it were me, I would just take a limo from the airport to the hotel. Walk up to Hertz at Brookfield Place the next morning and rent a car. Go visit whatever in MIssissauga all in that same day and return the car to Hertz and walk back down to the hotel. If I had to, I'd repeat that the second day. But then, I value comfort and convenience over cost more often than not. I like driving myself and am not bothered by driving in busy city traffic.