Yes, to avoid Toronto.
Not sure what route you're planning. US15 sort of dead ends in NY State on my maps.
After that, you're going to head west towards Queenston/Niagara Falls/Buffalo, to cross the border.
If you cross in the Niagara region of Ontario, and head west towards Hamilton, then take Hwy 6 north towards Guelph, and then stay on Hwy 6 northwards again towards Owen Sound, you could sort of start there, and either keep going up to Tobermory for a day/night, then work your way back down and around the Bay over the next few days. Or, just head east and start a tour around the Bay. No idea about classic cars, there might be some museums along the shore, and there's a rail line on the Trent Severn waterway that transported boats overland instead of by a typical locks system. You'll see more shipyards than train stations along the shore as you circle the bay.
Here's a google search link to some of the camping available around the area....
https://www.google.com/search?q=georgian+bay+rv+camping&npsic=0&rflfq=1&rlha=0&rllag=44724097,-80107215,32493&tbm=lcl&ved=2ahUKEwiz3IbmsbzhAhVL0oMKHX8LBD0QtgN6BAgKEAQ&tbs=lrf:!2m1!1e2!2m1!1e3!3sIAE,lf:1,lf_ui:1&rldoc=1#rlfi=hd:;si:;mv:!1m2!1d45.3445645!2d-79.61256139999999!2m2!1d44.4868822!2d-81.80006999999999;tbs:lrf:!2m1!1e2!2m1!1e3!3sIAE,lf:1,lf_ui:1Here's one for touristy stuff.....
https://www.google.com/maps/search/Tourist+Attraction/@44.880712,-80.2238799,9zGeorgian Bay is about the size of Lake Ontario, so it's not small.
It's not an easy question to answer because of the size of the bay.