According to the website 99scenes.com, Green Day is set to play OSHEAGA festival in Montreal, Quebec (Canada) this summer along with the band Phoenix. Here is what they had to say about the subject (translated by me):
Green Day will be headlining Osheaga 2013. Billie Joe Armstrong and his gang's last presence in Montreal dates back to 2010, when they played at the Quai Jacques Cartier. We found it weird that Green Day only had one concert in Quebec city for the ¡UNO!, ¡DOS!, ¡TRÉ! tour this spring. Everything is explained now that it is confirmed they will be headliners for Osheaga 2013.
OSHEAGA is known to be more of an "indie/hipster" festival, but have had more "mainstream" artists such as Snoop Dogg and The Black Eyed Peas these last couple of years, so everything is plausible.
OSHEAGA is normally held during the first weekend of August at Parc Jean Drapeau in Montreal.