Hi Marcus, welcome to Canada. There are a number of friendly airfields around the Toronto area, though I'm not aware of any who have a 182, that's not so common. I can ask about a R172K I know of, which might be available at Parry Sound, though that's quite a trip from Toronto.
You will find Orillia Lake st John very friendly, with the added bonus of both wheels and float flying at the same airport. 1.5 hour drive north from North York, but an easy drive, and very pretty in the fall.
Lake Country Airways: floatplane training, endorsements, float charters and rentals
Brampton Flying Club is the busy Toronto area airport, with many people to meet. It would be convenient for a Niagara Falls flight. Bear in mind that there are very strict procedures for safety reasons over Niagara Falls, failure to adhere will get you in trouble.
https://www.bramptonflightcentre.com/
Toronto City Center airport is a busy place, but much more Dash 8 commercial than GA now.
Buttonville airport will be closest to where you will be staying, there are lots of GA services there, though things are slowing, as that airport is planned to close.
Oshawa and Peterborough are good choices to the east, though at least half and one hour drive respectively. Burlington and Waterloo similar distances to the west.
Late September into October is just magnificent to fly around here, the colours are spectacular. For a whole day flight, (probably 4-5 hours) consider flying right around Georgian Bay, with a lunch stop in Killarney. You'll a good part of Ontario.