I haven't been on the stretch between High Falls and the Gauthier's Dam portage, but from there to the Nadine portage is wide, mostly lazy current Nipissing river. You'll have no worries about water levels. I was through there last July. 

Catfish Raps to Sunfish (assuming you're heading for the Newt portage?): I was through there in July of 2014 and while it's a narrow track through weedy water for much of it, there were no issues with water levels at the time. Jeff's map does warn it can be difficult in lower water conditions though so hopefully someone's been through there recently to give you more up to date information!

I was paddling Sunfish in extremely low water season, in August 2010, and it was passable, just thick with vegetation, as Martin mentioned.

I just got back from this area.  Some comments:
- I was going from Ramona to Nadine, but I did head up to High Falls.  Water levels are low, but were manageable for me.  You won't be able to paddle all the way to the High Falls portage.  I just abandoned my gear on a sand/rock bar and walked the last hundred meters to the portage.  I actually wish I had abandoned it earlier.  The low water is only an issue for the last few (maybe 400) hundred meters.
- Going from the Ramona portage to Nadine took me longer than I expected.  There were a few places where the water was low, and I had to wade.  I let the current take me, and I concentrated on steering around obstacles.  I traveled less than 3km/h (I usually average 5+), and it took me 1:45.  Usually I travel faster than what you find indicated on Jeff's map.  There's also a beaver dam you'll need to pull over.  In some places the current + wind was taking me nearly 3km/h so traveling upstream could be a slog.  The section below Nadine is more lazy.  You might consider reversing the direction of your trip.
- Going from the Petewawa into Catfish isn't a problem.  You only get into the marsh going into Sunfish.  I went to Sunfish, but I spoke to a couple who traveled that section of the Petewara and they said water levels were good.  Only the odd rock needed to be dodged.
- For those interested, the marsh to Sunfish is passable, but the weeds are pretty thick.  It just takes a little extra time.  You might also pass by the entrance to the marsh as the weeds are quite thick and the 4 ft. opening doesn't seem like it could possibly be the right route.

Some things to keep in mind:  I was traveling solo, and had a pretty light load, so I only need maybe 2 inches of water to clear obstacles.  Traveling Nipissing could be completely different in a heavily loaded canoe.

I didn't like the prospects of taking water from the Nipissing, so I brought water from Nadine (one of the clearest lakes I've seen).  The spring indicated on Jeff's map on the Nadine portage was nothing but a mud hole.

Hope that helps.