Browncoats rejoice! While very much not confirmed for the role of Nova as it's been previous rumored, [Castle](series:714842) star Nathan Fillion will definitely cameo in Guardians of the Galaxy, according to James Gunn himself:
“@STARS_TyranT: Are the rumours true that he has some part in the film?” @nathanfillion has a very small fun cameo he did as a favor to me." -- via James Gunn's Twitter
Fillion has been an iconic part of geek culture since his breakout role as Captain Mal in Joss Whedon's Firefly. This wouldn't be his first time within the comic book universe, either -- he's known well within the DC Animated Universe as the usual go-to for the voice of Hal Jordan, the Green Lantern.
While no details have been revealed as to what kind of part Fillion will play in Guardians, one can imagine that a one-off cameo may not lead to a full-fledged role as Nova in a future Marvel film. Who do you think we'll see Captain Mal play in [Guardians of the Galaxy](movie:424073)?
Guardians of the Galaxy releases August 1st, 2014.