Writer/director James Gunn has confirmed that the title of the third Guardians of the Galaxy film will be Guardians of the Galaxy Vol. 3. Gunn revealed it after a Twitter suggestion that he call it "Guardians of the Galaxy.mp3" from a fan.
I hear this suggestion a lot, from many different people. But, no, the three films are a set and I'm going to stay consistent with Vol. 3. https://t.co/jLGg625s4I— James Gunn (@JamesGunn) May 15, 2018
Guardians of the Galaxy Vol. 3 is anticipated to come out in 2020.