I paddled the Gatineau from Bouchette to Cantley in 2 long days. There's a pushy CII under the bridge in Northfield, be careful there since it varies quite a bit with water levels. Then a portage in Low. Take out in between the two dams and walk on the left dam road and about 1 km on river left to the put-in. The next swift is under the covered bridge in Wakefield. River right is easy, but watch for a fair size rock close to shore also on river right.
The section above Bouchette and below Maniwaki I have also done, many times, but with a different boat and purpose. Solid CIII and IV. Also varies a lot with water levels. Portages are well marked, but as mentionned be careful as you approach them.
I've never been on the river above Maniwaki and up to the Mercier dam (it's quite rough according to the map), or above the Baskatong reservoir. The section above Baskatong however is said to be really nice.
A very nice map "package" was produced a couple of years ago, and is available via La fédération québécoise du canot et du kayak at this address;
www.canot-kayak.qc.ca. It's for the Gatineau from start to finish, even includes an history booklet. Very well made.
Have fun,
J