Gallagher, who turned 21 Monday, had 15 goals and 13 assists in 44 games for Montreal this season.
Huberdeau had 14 goals and 17 assists while playing in all 48 contests for the last place Florida Panthers.
Saad notched 10 goals and 17 assists in 46 games for the Blackhawks.
Edmonton forward Nail Yakupov, last year's No. 1 draft pick, was not among the list of finalists despite tying with Huberdeau for most points by a rookie.
The Calder has been awarded to the top NHL rookie since 1933. Gabriel Landeskog of Colorado was last year's winner.
The NHL will announce the winners of all awards at some point during the Stanley Cup final.