First let me say that I like twisty roads with less traffic, I ride reasonably fast and enjoy eating up the miles. I find the Eastern rides much nicer and faster with less traffic and more open spaces than the West. In my opinion the route I am suggesting would be classed as a hard assed ride on a vintage cycle that would take the 6 hrs you are looking for. You will not stop smilling.
Okay heres my suggestion follow it on Google maps.
Try to take a fast direct route to Bobcaygeon, I can lay a route out for you to get there if you wish.
From Bobcaygeon
Take Hwy 36 N/E to Flynns Turn.
Take Hwy 507 N/E to Gooderham
Nice cafe at intersection of 507 & 503
Take Hwy 503 to Tory Hill
Take 118 North to Essonville
Take Hwy 4 East to Wilberforce
Take Hwy 648 N/E to just past Harcourt
Take Hwy 10 North ( Elephant Lake rd / Petersons rd N/E to Maynooth
Take Hwy 127 North to Hwy 60
Take Hwy 60 N/W into the park
I can suggest nice routes to Bobcaygeon, we take a very nice direct route as the fun really starts at Flynns Turn. On the way back there are some really nice roads just west of the park that I am still finding but Im sure a more local lad can help you on the return route.