Louisa does have pretty good lake trout fishing in it, we base camped on the large northerly island last year. Pretty lake and VERY deep. It can be reached from PP in one day, Louisa falls portage can be taxing though. We saw only one canoe go by when we were there.

The S chain is a nice route option as well. It depends on the time of year you are planning on going through, but you can get solitude there and the fishing is pretty good.