Petawawa River
This is some of the best whitewater in southern Ontario (yeah, we consider Algonquin still southern Ontario). The best experience is at least five nights putting in at Brent on Cedar Lake and taking out at Lake McManus. Or, you could put in half way down at Lake Traverse. If you really boot it, you can do Traverse down in two nights.Â
Most of the runnable whitewater is 'drop and pool', which means fun but short rapids.