Are you sure you have stunted bluegills? If so, northerns or even musky won't solve your problem IMHO. As they get larger they will just target your larger bluegills and smaller bass. Mostly likely the bass as they are more fusiform. LMB are a much more effective bg predator.
What are you goals? Bass pond? Large bluegill pond? Both?
I would add more bass myself if i wanted to get the bluegills in check if that indeed is a problem Get a thousand feed trained bass from Laggis fish farms in southwest Michigan in the spring. Feed them in a cages for the summer until the fall and then release them. (If you don't cage them they will be larger bass forage). They'll start on your smallest bluegill and will go after progressively larger ones as they grow which will be rapidly.
If later on you feel you have too many bass due to lower relative weights you can easily cull them.
