I'm going to go with a less obvious choice here and say Scott Stevens. Could you imagine a Stevens in his prime with Komisarek under his wing? That would be one scary duo. Not one season was he ever in the negative for +/-, and that is insane for a defenceman that plays 30 mins a game. He could turn the tide with a bone crushing hit (i.e. Lindros, Kariya - yes he did score later that game but wasn't the same the rest of the series), and he also put points up. With Markov, the Habs could be like Anaheim, able to have 2 great defencemen that are able to play 30 mins each which means either one of them is on the ice almost the whole game which would definitely bring down the mistakes.
Another good choice would be Messier in his prime, huge centre with great leadership qualities, the power forward of his generation.
Can you imagine The Rocket in a Habs uniform right now? He would grab his own players by the throat and make them perform. He was like Claude Lemieux if Lemieux wasn't a coward and Michael Bossy: Killer instinct and mad skills for scoring in one body.