The league announced the finalists Monday. The winner, voted by general managers around the league, will be revealed June 18 at the NHL awards show in Las Vegas.
Mason, a rookie, posted a franchise-record three straight shutouts in December and helped the Blue Jackets reach the playoffs for the first time. Thomas led the NHL with a 2.10 goals-against average and a .933 save percentage for the Eastern Conference-leading Bruins.
"It's quite an honor," Thomas said after the Bruins practiced at Ristuccia Arena on Monday. "Just breaking into the NHL a few years ago, you're always trying to make your goals bigger but you want to make them reasonable. You know, one step at a time."
The Bruins, who completed their Eastern Conference quarterfinal series with a sweep of Montreal last Wednesday, won't find out who they're going to play in the second round until Game 7 of the Carolina-New Jersey and New York-Washington series are completed Tuesday night.
The Bruins can play Pittsburgh, Carolina or New York.
"Being a Vezina finalist was always off my radar," Thomas said. "I think as the year went on this year I realized that there might be a chance. But it's quite an honor."
Backstrom appeared in 71 games for Minnesota and ranked among the top five goaltenders in goals-against average, save percentage and shutouts. His 37 wins were a franchise record, and after playing in his first All-Star Game he received a four-year, $24 million contract extension that will begin next season.
The 31-year-old has experienced a sharp increase in attention since he first signed with the Wild as an unknown backup out of the Finnish Elite League in 2006, but Backstrom said he takes these honors and awards in stride.
"You don't really think about those things," Backstrom said by phone from Colorado, where he's rehabilitating following hip surgery. "It's more you focus on your game and try to help your team."
The surgery showed less cartilage damage than expected, and Backstrom is on track to be at full speed in three months -- about half the time it could have taken to recover.
"For sure, it was great news for me," Backstrom said.