I'd throw the bank at Vanek. He's a reliable player and hasn't show any signs of slowing down. And he's 29, to boot!
Gaborik would be nice but the guy has had a history of dealing with injuries, especially with his groin. Nevertheless, he's another player, I'd try to get with a 5-year contract.
HOWEVER...
Next year, the only forward whose contract will run out is Gionta. Sure, 5 million is a lot of money, but PK Subban will need to be re-signed and that 5 million cushion will be going towards that.
Meanwhile, Markov's (almost) 5.8 million contract will end. I'd be weary to sign him at even half of that amount, now. Emelin's contract would also need to be re-signed as well.
Bottom line ; I don't think the Habs will be in any position to go after *any* high-profile UFA. The Brière and Desharnais contracts will make sure of that. Bourque's contract doesn't help either.