Engagement

Caledon Country Club, Mount Alverno, or any golf course really should be able to support hosting outdoors. Or I've seen estate properties do air bnb events as well and that way you can have your own tent, catering etc

What's your budget? Because any gathering in Ontario where guests are eating have to be a seated event, regardless if it's outdoors or indoors (no cocktail hour style parties allowed). So unless you're hosting an event without food or drink (which imo will not be very appealing), you're pretty much looking to either pay for a plate per person in some way. This could be at a restaurant, a banquet facility with outdoor options like golf courses and country clubs, or a private property like a farm with catering. Maybe try some of the golf courses in the area first, like Mississauga Golf, Credit Valley, or Lakeview.