Earlier today, I wrote a story in which I speculated that Captain Marvel/Carol Danvers might be James Gunn's favorite superhero and that would mean that she would appear in Guardians of the Galaxy 2 - based on his recent hints. After the article was posted Gunn was bombarded with people asking him if that was possible. He replied with this tweet, "Still wondering if Captain Marvel will appear in #GoTG2" Getting this a lot this morning. As I said months ago, no, sorry."
Welp, no harm in speculating. Let's look at it from the bright side, we now know Captain Marvel isn't Gunn's favorite superhero and she won't be in Guardians of the Galaxy 2. That means, we can keep trying to piece together that puzzle. You're welcome!
Another rumor that is supposedly circulating is that Symbiotes could appear in Guardians of the Galaxy 2, but Gunn snuffed that rumor out too. It is probably being mentioned as a possibility because of "The Planet of the Symbiotes" story arc in the Guardians of the Galaxy comic books. Comic book writer Brian Michael Bendis kicked off that storyline in November of last year and it has gone over incredibly well.
This should also be mentioned, in the past you could strike down such a rumor with ease because Sony has the rights to Venom which more than likely includes anything symbiote-related. BUT, Sony and Marvel recently struck a deal that will allow for their characters to crossover, so it is possible. In my opinion, it would be a clever way to plant the seeds of Venom for Marvel's new Spider-Man.
“@Ali_Akhtar_: what about the symbiote rumours?" There are no rumors. Just guesses, which are fun. Only 6 of us know who's in GotG2.— James Gunn (@JamesGunn) March 7, 2015
Marvel’s “Captain Marvel” will arrive in theaters July 6, 2018. Guardians Of The Galaxy 2 will arrive in theaters May 5, 2017.