The film, which was formerly known as "The F Word," was written by Elan Mastai and concerns Radcliffe and Kazan, who meet at a party and are attracted to each other. A romance is hindered by the fact he has recently ended a relationship and she has a boyfriend (Rafe Spall), so the two attempt to be friends.
Directed by Michael Dowse, "What If" also features Adam Driver (Mrs. Warren's Profession, Man and Boy), Mackenzie Davis, Megan Park and Oona Chaplin.
Radcliffe has performed on Broadway in Equus and How to Succeed in Business Without Really Trying and will star in Martin McDonagh's The Cripple of Inishmaan in April. His film work includes "Harry Potter," "Kill Your Darlings," "The Woman in Black" and "December Boys."
Kazan's stage acting credits include Come Back, Little Sheba; The Seagull; and A Behanding in Spokane. Her playwriting credits include Absalom and We Live Here, and her film writing credits include "Ruby Sparks," in which she also starred, and "Revolutionary Road," "It’s Complicated," "The Exploding Girl" and the HBO miniseries "Olive Kitteridge."