During a press tour for his appearance in the upcoming film Jurassic World: Fallen Kingdom, actor Chris Pratt disclosed to MTV International that Guardians of the Galaxy Vol. 3 will begin filming in January 2019.
Here's a video of the interview. Pratt reveals the Guardians Vol. 3 start date while attempting to avoid revealing Avengers: Infinity War spoilers.
In a seperate interview, Jeff Goldblum - who returns to the Jurassic universe with Fallen Kingdom - seems to confirm his Grandmaster and Benicio del Toro's the Collector are brothers in the Marvel Cinematic Universe ala the Marvel comic book universe.
Guardians of the Galaxy Vol. 3 does not have a confirmed release date.