Just like the comics, I mean he has the power to quite literally rip a symbiote from it's host.
http://i230.photobucket.com/albums/ee217/Darkhalen/spiderman-web11927.jpg
Like TAS, I doubt that but I hope he is not used, it then becomes more a case of, oooh Carnage is in it I like carnage, let's go see that, once they have, oooh it wasn't any good Carnage is not in it very long, he is dumbed down, its not about Carnage its about Venom, it's named after him, and he is the star so why should Carnage oust him out of the spotlight of his own film.
The only problem with Venom is tragically, it has become more a case of Venom & Carnage rather then just Venom on his own, and it seems you can't have one without the other, no matter how much we despise the latter of the 2, I find it sad that Venom has to always share his glory with Carnage, I mean Carnage got his own 14 issue Comic, what does Venom get, barely nothing worth of screen time in Spider-Man 3, I am afraid that may be the case with the Movie.