I've always thought that players should vote for their captain. The role should be filled by someone who can lead his teammates, it's not a fan-popularity contest.
Having said that, there's no obvious candidate to fill the role currently on the Canadiens. Andrei Markov could be the guy, except that he'd struggle with the media demands, and he doesn't suffer fools gladly. If he'd accept the role, it'd be great, no one can question him on talent or effort or experience or dedication. He wouldn't be a warm and fuzzy captain like Trevor Linden or Yvan Cournoyer, he'd be more of the Chris Pronger mold, a do-as-I-say-or-else guy. Which isn't necessarily a bad thing, leadership comes in many forms.
I don't think P.K. is ready. He has through his short career been loquacious, intentionally controversial sometimes. He has played the role of lovable buffoon, and we've seen his teammates be hard on him at first, then loosen the leash somewhat, but still try to keep him in line, and deflate his his ego, through humourous putdowns and pranks as seen on "24CH".
He can transition into a leadership role now, with his contract in hand and status assured, and also because a vacuum has been created by the departure of Josh Gorges, Brian Gionta, Francis Bouillon, among others. He can take a step forward, and instead of hamming it up for the cameras and the fans, can play the role of exemplar for the young defencemen coming up through the system. He has more experience, fewer veterans in front of him, he can be less the "Yes, Sir!" rookie type, and more of the "Watch me go" player.
All of us who've been involved in team sports know this dynamic, how when you first join the team you're supposed to fight for a roster spot, for playing time, you observe the veterans and do as they do. A couple of years later, you're one of the boys, you know your stuff, and you try to take rookies under your wing, show them the way, you speak up when necessary. This is a natural, normal progression. Often, you don't even think of this process, you're just nudged in the right direction by the team dynamics. As a newcomer you can be the ingratiating jokester, but as you become a veteran you tone down that act a bit to lead your teammates, because that's what is needed, you don't necessarily need to be told.
So Andrei would be a great transition captain, he can serve two or three years, and then the title can be handed off to the next player who imposes himself as the dressing room and on-ice leader, whether that is Max or P.K, or by then Alex Galchenyuk, Brendan Gallagher, Jarred Tinordi, etc.