On the surface, he shouldn't "need" retention to get a 1st round pick in return. $4.4m for next year, for what he brings to the table, is something a lot of teams would make the room for. Especially with the cap getting another big bump this summer.
Heck, from the Leafs standpoint... go and get him to pair alongside Rielly, leaving you with a McCabe-Tanev and OEL + Benoit or Hakanpaa as a 3rd pair, and I think that's a really difficult group to match up against.
The challenge for any aquiring team will be fitting him in this year, as most teams aren't carrying / banking $1m+ in cap space to be able to add a player of his hit at the deadline, nor do they have $4m of "dead weight" that they'd be willing to send back.
It's probably the kind of situation where you have to wait until the deadline, to see who has the LTIR space to squeeze him in for this year. Even then, maybe you retain, but I'd imagine it'll be a 1st + at that point... given it'll be an extra year at just $2.2m.