Executive Producer Victoria Alonso states filming to start in June:

“Production has already started! Completely. It started months ago and we have an entire team in London already – we start shooting in June. Our director [James Gunn] travels next week and it’s going, baby! It’s a fast train to a beautiful place.”

via ScreenRant.

Executive Producer Victoria Alonso explains the plan for bringing Groot and Rocket Raccoon onto the big screen:

You can’t do any motion capture with a raccoon – they won’t let you put the suit on [laughs]. But we will do rotomation, probably, for some of the behavior. Rocket will have his own personality, of course, and clearly we can’t do mocap on a tree, per say, but we definitely will have performers to emulate what James Gunn will lead to be the behavior and the performance. He’s very clear on where he wants to take the characters.

via Collider.

Jason Momoa, though not yet officially confirmed, is strongly rumored to take the role of Drax the Destroyer according to Latino Review:

According to the report, Momoa won Marvel’s attention with an impressive screen test and they immediately offered him the part. He’s currently in negotiations to join the James Gunn written and directed film.

via ScreenRant.