Another thought: the Manigotagan is one of the southern-most rivers flowing into Lake Winnipeg. There is a very good website covering the river at this site. I am really excited about the prospect of trying this, and so is James. Starting point would be Caribou Landing at Quesnel Lake.
An overview of the trip, using waypoints provided by Manitoba Eco-Network.
View Manigotagan River Trip Plan in a larger map