Mississagua River - Mississagua river flows from Mississagua lake into Upper Buckhorn lake situated minutes away from Buckhorn, ON. For a few weeks in the spring this gem of a canoe route becomes a great whitewater run with plenty of rapids ranging from class two to class five. All of them are scoutable and can be conveniently portaged. Most people portage at least part way two most challenging rapids - falls and Scott dam. A number of other rapids should be scouted as well. Beware of wood in some spots.
This river also has an option when the Trent-Severn is drawing down water in the fall. The river in this state is a far different character in lower water, but still challenging. Be wary of the costs parking at the take out when the provincial park is in operation.
(Copied from Whitewater Ontario's old River Wiki page)