Re: kennebec river
If this is your first trip or if you don't have much time you may want to stick to a simple plan (The Kennebec) but if you like to explore I am giving you some things to ponder below.
There are other streams in the general area that would provide good trout fishing. As Pocono said you need to be a good distance up channel to find trout water and depending on the weather and when you visit the out flow at the Lake can be pretty warm. This will move the trout and salmon down river into deep pools and to the mouths of tributaries.
If I were going to fish for trout I would check the regulations (to be sure it's open) and plan to fish Ragged River out on the paper company lands. You can find this by checking a map and tracing the road from the Kennebec (Jackman) to Greenville, and then from Greenville to Big Eddy. You will find the Ragged crossing the Golden Road about twenty miles or so past Kokadjo. It has been 15 years since I was last there but this was a great place to fish. Prior to my moving away from my home in the North East I fished up there every time I could get away to do it. The stream I am advising sees very little in the way of fishing pressure and is home to some big Brook Trout and gets Landlock Salmon in the fall.
If you want any tips on the water release schedule for the rivers (safety first) check with the security person at the gate to the Golden Road.