Two Cassavetes films, two lead performances by Gena Rowlands that bookend Cassavetes' output in the 1970's. Both of them play with what we know about the actors real lives, and Cassavetes uses those things to drive excellent performances from all of the actors, and each of them are notable for having incredible supporting performances. Should Minnie and Moskowitz, with its more focused and easily digestible narrative make the Canon, or should it go to Opening Night, the intense psychological character study?
Both of those would be excellent too! I put forward Minnie and Moskowitz/Opening Night because they bookend Cassavetes' output in the 70's but really there are loads of Cassavetes' films that are canon-worthy
Or A Woman Under the Influence.