I've done that many times and live in Mississauga. Check out the sticky in this forum for lot's of ideas - I've copied the section about the Parry Sound / Huntsville area directly below. If you do the route below, it will be much better than what you have suggested.
I have not been up there this year so I can't comment on road conditions. I usually eat breakfast at home, bring snacks and find a nice scenic spot to eat my bagged lunch. You can easily get gas in Parry Sound or Huntsville. I think someone once posted up that there is an excellent bakery in Orville along the 518, but I have never been.
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Parry Sound/Huntsville Area Roads: ride a bit further north or east than the roads/route mentioned above and check out some of these other roads mentioned below:
Hwy518 is a very nice technical road - the best parts are between Orville and Sprucedale. From one side to the other, this runs east/west from Parry Sound and even crosses over to the east side of Hwy11 for some more good times. There are sections with fast sweepers, other parts with twisty technical stuff and some dirty curves with frost heaves.
Chetwynd Rd is a great run that links up with the Hwy518 on the east side of Hwy11
Tally-Ho / Swords Rd is a short ride between Hwy518 at Orville and Hwy141.
Ravenscliffe Rd is a great road intersecting Hwy518 at Sprucedale and runs all the way to/from Huntsville. There is a nice scenic pull off/ boat launch at Buck Lake.
McDougall/Hurdville Rd combo is a nice and hilly twisty stretch just northeast of Hwy518
The Bunny Trail north of McDougall is a piece of paved flat out fun.
Hwy520 is a nicely paved road from Hwy11 to Magnetewan with fast sweepers.
The Old Nippissing Trail is an amazing twisty, hilly run that changes between paved, chip-seal, hard packed gravel and hard packed sand. Apparently it runs north/south from around Commanda, through Magnetewan, and meets up with Hwy518 near Seguin Falls. The most passable section by streetbike is south of Magnetewan, with some awesome sections of non paved stuff in there too. It was an old pioneer horse/carriage rd and is considered a heritage rd or something like that. It's very technical and of my favourites.
Intersecting Old Nipissing Trail is
Orange Valley Rd leading to Broadbent Rd which are nice hard packed gravel roads with some nice twists.
Further north and starting east from South River, is a great loop including a road called
Chemical Rd / Deadhorse Trail. If you don't mind a little hard packed dirt, then it leads to the Deadhorse Trail, which is a fun ride to the western edge of Algonquin and then works its way back to Sundridge or you can work your way further south to Chetwynd Rd. In some spots it's like a 2 track ATV trail at times, so you can touch the leaves of the trees as you ride past them. It can get a bit slippery when wet, but when it's dry, it's lots of fun!
Parry Sound / Huntsville Area Route: Here's a route of the paved roads above between Parry Sound and Huntsville which can be done from the GTA in around 10 hours.