Sharks skipper Gallen and Tagataese, both having completed training yesterday, are set to return from respective back and shoulder injuries to take their place against the Cowboys.
Gallen missed Cronulla's qualifying-final win over Canberra a fortnight ago, while Tagataese hasn't played for five weeks.
North Queensland have also rushed Kane Linnett straight back into the centres. He's overcame a hamstring injury that had kept him out of last week's semi-final win over Brisbane.
Linnett takes the place of gun rookie Kalyn Ponga as the reigning champions continue their quest to become the first club to claim back-to-back titles since 1992-93.
"He's got a few things he has to tick off but he's likely," Cowboys coach Paul Green said.
Green also said injured winger Antonio Winterstein was an outside chance of recovering from a rib problem and would be given every chance to prove his fitness.
Winterstein and Ponga will travel with the team today to Sydney.
Melbourne have listed Christian Welch as the replacement for injured giant Nelson Asofa-Solomona, but have also added Felise Kaufusi and Matt White on an extended bench.
Asofa-Solomona last week was ruled out for the rest of the finals series with an elbow issue.
The Storm take on a healthy Canberra squad, unchanged from the one who knocked Penrith out of the premiership race last week in the nation's capital.
Saturday's grand-final qualifier at AAMI Park will be the Raiders' first appearance in week three of the finals since the Super League competition in 1997.
They are the last of the current 16 teams to feature in a grand-final qualifier in the NRL era.
The grand final will be played on Sunday week at ANZ Stadium.