Best parks for backpacking?

Forks of the Credit Provincial Park, about a 45 minute drive north-west of Toronto, has everything you're looking for: trails, waterfalls, camping, fishing, and much more.

http://www.ontarioparks.com/park/forksofthecredit

Before you leave the area, be sure to take a 5 minute detour to visit the Cheltenham Badlands

Finally, no trip to the Forks of the Credit would be complete without getting a hot beverage at Higher Ground Coffee, which is often frequented by motorcyclists.

Higher Ground Coffee Co. Belfountain

https://www.google.ca/maps/place/Higher+Ground+Coffee+Co.+Belfountain/@43.794236,-80.014409,3a,75y,33.47h,77.01t/data=!3m4!1e1!3m2!1sdA0VZKehl2aPbgjV6W23UA!2e0!4m6!1m3!3m2!1s0x0:0x2b5feb05881858df!2sCheltenham+Badlands!3m1!1s0x0000000000000000:0xb2389be19744c2f1!6m1!1e1

Hey Greg, can you specify, by backpacking do you mean hiking, camping/sleeping outdoors or light travel and staying in low/no cost accommodations? 

Toronto is a pretty urban center and there is the Glenrouge Campground Glenrouge Campgroundwhich I can't vouch and don't know anyone who has stayed there. There are lots of great hiking trails like the Lower Don River Trail High Park to explore.

But for camping most Torontonians head north to areas like Wasaga Beach Orillia or even farther north to Parry Sound or north west to Bruce Peninsula National Park to get out of the city and past the farmland.

I will suggest you to go for Glen Stewart Ravine. It is one of most ideal one destinations for hiking or adventure lovers. There a visitor could enjoy rich charm of nature with divers plants and birds species and if you are a nature lover, then you must visit there in the spring season. It offers majestic views there.I had great experiences after completing my tour, http://www.getbustours.com/3day-boston-washington-baltimore-philly-york-tour.html years ago.  

There are not a lot of backpacking alternatives near Toronto. The GTA (Greater Toronto Area) is home to over 6 million people. Some areas you might want to check out are the Bruce Peninsula National Park (closer to Toronto) and Algonquin Park (about 3 hour drive north of Toronto).