Garon is a quality backup goalie - one of the best in NHL. He shouldn't have any problem finding a job in the summer. But at the same he's only a backup goalie so do not expect much from him.
Montoya - you're absolutely right in selling him with the first chance you get. He's nothing spectacular and I doubt he's in the NHL next year. Career journeyman backup goalie at best.
Dubnyk is your best bet and only one of these with a starter potential. He's locked up through next year and has to compete with Khabibulin and Khabby's done. Hard to tell about Dubnyk's future in the long-term but he has a potential to be a starter in the league. He's by far your best option here.