I'm on the de Haan and Czarnik train.
I'm guessing de Haan would make a nice defensive counterpart to Vatanen as a first pairing. It was a while ago, but Greene and Severson worked well together in Severson's first season. They may still be able to handle 2nd/3rd pairing duties. Butcher paired with either of our remaining defensive defensemen (Santini or Mueller) would work for me too.
Carnik's not guaranteed to be a player, but I think it's worth a shot to give him time with some real linemates. He was buried on the Bruins because of their RW depth. He may be a too small to be effective, so it's definitely a gamble. We can really use the RW depth.
That being said, I suspect we're going to pick up a player NO-ONE here expected.
-edit-
It would never happen, but I'd also love to offer-sheet Slater Koekkoek in Tampa, or trade for him on the cheap. Maybe we can pry him away if they win the JT sweepstakes.