Star-Lord, Gamora and Drax will be at the centre of the film and will receive "visual and backstory updates", Latino Review claims.
Gamora and Drax both have links to the villain Thanos, who is expected to appear in the movie following his Avengers cameo.
The former was adopted by the Titan, while Drax the Destroyer is a being who was created specifically to destroy him.
Rocket Raccoon and Groot are non-humanoid characters, and expected to receive less focus than their co-stars.
James Gunn will direct the movie based on Dan Abnett and Andy Lanning's Guardians of the Galaxy comic run, which dealt heavily with the death and return of Thanos.
A new Guardians of the Galaxy title from Brian Michael Bendis and Steve McNiven was confirmed for Marvel NOW! at New York Comic-Con last weekend.