Vin Diesel will give his voice to Groot again in Infinity War.
Zoe Saldana is returning as Gamora.
Karen Gillan is returning as Nebula.
Brie Larson will be a new character Carol Danvers / Captain Marvel in her first Marvel movie Avengers: Infinity War.
Pom Klementieff we will meet her as Mantis in Guardians of Galaxy vol.2 and after that in Avengers: Infinity War.
Sebastian Stan is coming back as Bucky Barnes / Winter Soldier.
Bradley Cooper is giving his voice to Rocket Racoon again.
Samuel L. Jackson is returning as Nick Fury.
Dave Bautista is Drax the Destroyer.
Paul Rudd is Scott Lang / Ant-Man again in Avengers: Infinity War.