"It's going to be a really surprising open. What happens is all the characters are killed in the first 10 minutes," Gunn joked. "In really horribly brutal fashion."
Jokes aside, Gunn confirmed that all five original Guardians will be back, along with unspecified other characters from the first film, and that fans may see the team adding members. Gunn also said the new film will uncover some secrets posed in the first.
"I spent all day on Aug. 1, the day the first movie was released, writing 'Guardians 2,'" Gunn said. "I was so excited about it and I was finally able to let go of the last one and begin the second one. I always saw this as a universe, not just as one story."
[ Read: Review of Guardians of the Galaxy ]
He also talked about what to expect from the upcoming DVD release of "Guardians," which will arrive in stores Dec. 9. In addition to a director's commentary, Gunn promised a number of deleted scenes that he said add to the background and context of the characters rather than distracting from or changing the story. He particularly likes a scene where Rocket Raccoon (Bradley Cooper) fakes a laugh at Peter Quill's (Chris Pratt) plan.
"In the long version of the scene where Rocket is laughing at Quill, Quill gets very offended by that and takes a vote of the other Guardians to see who thinks that the laugh is fake," Gunn said. "It's a pretty fake laugh, and I think Rocket gets hurt that Groot goes against him."
Gunn also discussed his passion for making the film in 3D, which he said was a decision he pushed for from the beginning of production. He got his way and he believes that the 3D release is one reason the film continues to see success worldwide. Gunn said it's that international appeal that drives the decision for a studio to go 3D with a film rather than what a director necessarily wants to do with it.
He said, "3D kind of is a wash in the United States, but in Europe it's bigger. So it makes much more of a difference than it does here. If it was just 3D in the United States, most people would not do 3D."
Unlike films that simply apply 3D in post production, Gunn planned the film and its effects for the 3D experience. This meant avoiding things like shaky cam in action shots. He said his special-effects training came on the set of "Scooby Doo 2: Monsters Unleashed," which he wrote, when producer Charles Roven brought him on set presumably to groom him for directing a possible third movie in that series. Gunn said that VFX experience helped him understand what works and what doesn't with CGI. It also led to his decision to cast his brother, "Gilmore Girls" actor Sean Gunn, as the motion reference actor on set for Rocket Raccoon rather than just using a prop stand in.
Some of the film's technology, including the use of 3D printing to produce the guns, was a new experience for Gunn.
While not necessarily taken aback by the critical success of "Guardians of the Galaxy," Gunn said he was surprised and enthused by the excitement its generated in fans, especially the ones who have gone to see the movie multiple times.
Despite that excitement surrounding the first film, its planned sequel and Marvel and Disney's proven success with crossing characters over between movies, Gunn said a crossover with one particular Disney property was unlikely -- even if his characters do have the ability to travel to galaxies far, far away.
"'Star Wars' was a long time ago," Gunn said. "It would have to be time travel."