Maggie Gyllenhaal and Peter Sarsgaard have booked roles in the upcoming Off Broadway production of Anton Chekhov’s “Uncle Vanya” at Classic Stage Company.Duo joins a cast that includes Denis O’Hare (“Take Me Out”) in the title role, Mamie Gummer (“Les Liaisons Dangereuses”) and George Morfogen. Sarsgaard is appearing in Chekhov’s “The Seagull” on Broadway in a run ends Dec. 21. Gyllenhaal’s stage credits include a staging of Tony Kushner’s “Homebody/Kabul” that played L.A.’s Mark Taper Forum in 2003 and went on to the Brooklyn Academy of Music in 2004. Gyllenhaal plays Yelena, the pretty sister to Gummer’s plain sister, Sonya. Sarsgaard portrays the doctor Astrov. Helmed by Austin Pendleton (“50 Words”), “Vanya” runs Jan. 17-March 1 at CSC.