Hey, I haven’t paddled that section but I have planned it.
From Mattawa to Pembroke it is 200km. In the years past I have become a down river paddler with little inclination up go against the river. How long this would take is dictated completely by how many days you want to paddle for? I paddled from Pembroke to Ottawa and that too is 200km, and it took 8days with no rest day. We started April 17th and when we reached the gauge in the Ottawa River Provincial Park it read 18 Â½. If you are inclined to do this route look for Hap Wilsonâ€™s books on Ottawa Valley canoe Routes.
Look at http://www.myccr.com there may be some assistance for you there.