First off MN_Rebel is right, it counts to your limit if you keep fish (I also live in MN)
HOWEVER if your a loser like me and you only fish to stock your tank, your not worried about keeping your limit because you wont be fishing again anytime soon, at least not to keep the fish
Heres the deal, you can do that and keep a northern however you should just be aware its going to turn into a big beast and it is possible it's going to destroy the other things it is with (eventually)
All that being said, I say do it! Give it a try!