We actually already knew that James Gunn had some part to play with the development and production of Infinity War, as he is credited as an Executive Producer on the project.
Infinity War is just around the corner, and it will bring a number of team-ups between its heroes that we have never seen before.
As it turns out, James Gunn played a part in the writing process of the movie, at least for the parts the Guardians of the Galaxy were involved with.
From watching the trailers and leaked footage of Avengers 3 that included the Guardians of the Galaxy, it becomes notable that James Gunn did have something to do with the writing.