Following the events of Avengers: Infinity War we have no idea what's next for the Guardians of the Galaxy, except that there will be a third film, which James Gunn is currently writing. While the writer and director of the next movie certainly isn't giving away any spoilers, he did recently respond to fans on social media and about the writing and directing process and has revealed a handful of pieces of information regarding the script, the soundtrack, and the shooting schedule. Most interesting, the director says the new Guardians movie will be very different from its predecessors. According to Gunn...
Of course, there is one major way that we can think of that would make the new movie very different, which is the possibility that the makeup of the team won't be the same. Following the events of Avengers: Infinity War only Rocket is actually still alive, and while we have every expectation that the actions of Thanos will be reversed to some degree, it's far from certain that the entire Guardians team will make it out of Avengers 4 alive.
Beyond the general ways that the new film will be different. Gunn also revealed chatting with fans on Facebook that the soundtrack for Guardians of the Galaxy Vol. 3 is mostly complete, though it's possible the soundtrack could go through changes as the script does, and Gunn says he's made a lot of changes to the script.
James Gunn also tried to manage expectations by saying that even if the proposed Disney/Fox merger goes through before Vol. 3 is complete, fans shouldn't expect it to impact the new film in any major way, as it's already too far along for those sorts of things to have an impact. He does say he has chosen all the characters who will appear, though of course, he doesn't let on as to who they may be.
In a separate conversation on Twitter, James Gunn revealed that he expects Guardians of the Galaxy Vol. 3 to take about five months to shoot. That's the approximate amount of time the other two films have taken, and while Gunn calls the next movie "more complex" he apparently doesn't think the added complexity will add to the schedule in any significant way. And again, he doesn't explain why the new film will be more complex. Any sort of complex visual effects would only likely increase the post-production period, not the shooting schedule. Perhaps the new movie will require more locations and have many more characters, which could potentially increase the time it takes to film.
Guardians of the Galaxy Vol. 3 is expected to shoot next year for a release date in 2020.