UPDATE (kr time feb 26; 11:30)
The Korea article was wrong. The director of the movie posted on his me2day (korean version of Twitter) and explained that Siwon will not be in the movie (it seem like he was supposed to. Probably his drama schedule made it impossible).
Original source Jang Jin Official me2day
Translated by Alice (`Whiteuk별♯♪) @ sj-world.net
Actor Kim Sooro & Han Jaesuk and Super Junior Siwon have been casted for the new comic movie called “Quiz King” of the director Jang Jin. A person in charge of the movie said “Director Jang Jin and the actors are reading the script and they plan to film the movie soon”.
“Quiz King” is a movie about 6 blockheaded guys that get together by a traffic acident, they all want to have as much money as a lotto’s prize so they participate in a quiz show, all of them know the answer for the last question by chance and the movie is about their individual struggle to guess the right answer for the previous questions.
“Quiz King” is planned to start filming in March.