Hard to beat Lake Umbagog National Wildlife Refuge. The state of NH has remote campsites located around the lake, they are primitive, just a cleared spot and maybe a picnic table. There is power boat traffic on the lake but nothing compared to southern NH. There are some nice paddles up the Magalloway with some slightly faster water.
Richardson Lake, just over the border is even wilder than Umbagog, there are some primative sites administered by South Arm Campround that are very well spaced. Richardson has some incredible sandy beaches later in the season (they are both hydro dam controlled lakes so the water level varies seasonally).
Last place to go is Flagstaff lake in Maine (a couple of hours east), you can camp anywhere as long as you dont have a campfire. There are a couple of established sites but most just pull up a stretch of shore. No cost for camping and no services. Due to its depth and large maount of floating obstructions, power boats rarely go on the lake.
Both lakes are large and relatviely shallow plus oriented to get the breeze/wind in the afternoon so it can get choppy especially in the afternoon. Many mornings, they are "glass"