Confirmation that a Guardians of the Galaxy video game is in the works comes from a list of games from the Screen Actors Guild - American Federation of Television and Radio Artists, which is a union for voice actors.
Warped Zone points out SAG-AFTRA authorized a strike against various video game developers and production studios nearly two weeks ago, and released a list of games that won't be struck against, with Guardians of the Galaxy being among them.
As noted, it's unknown what platform the Guardians of the Galaxy video game will be available for, as it could simply be a mobile game, but it could very be well the TellTale Games' unannounced Marvel game as the Guardians of the Galaxy video game shares a production house with Telltale Games' The Walking Dead: A New Frontier.
Guardians of the Galaxy as a video game from TellTale Games would be an interesting choice as their previous games, including The Walking Dead, Batman, Game of Thrones, and Borderlands, are known for being rather dark, gritty and realistic. While the 2008 comics that inspired the Guardians of the Galaxy movie would fit in rather well with that approach, the movie, animated series and recent rebooted comic book has actually been quite the opposite with more of a goofy Looney Tunes approach.
Again, it's possible the Guardians of the Galaxy video game could be some sort of mobile tie-in to Guardians of the Galaxy 2, but a TellTale Games version would be damn cool (and they could even use Richard Rider Nova who appeared along side the Guadians in the comics).