Why have one actor play your lead character when you could have two? That’s the central conceit of this distinctive Canadian indie, written by the actors in question, Amy Nostbakken and Norah Sadava, and adapted from their stage play. They are both Cassandra, a disorganised woman in Toronto thrown into crisis by the death of her mother. Unlike movies with similar conceits – Luis Buñuel’s That Obscure Object of Desire, for example, where two actors alternated in a role – Mouthpiece keeps both women on screen at all times. As a reflection of a fractured mental state, it’s an effective device, although the relationship is not sharply defined. Sometimes they are like best friends or sisters, in playful internal dialogue; others they are in good cop/bad cop opposition, or even conflict. Sometimes their movements are identical (they trip over their scarves in synch, for example); at others they appear to be autonomous. The comic potential of the setup is largely sidestepped although a highlight is a scene where one Cassandra chimes in with distracting criticisms while her other self is trying to have sex with an old flame.

As the Cassandras traverse snowy Toronto, making preparations for the funeral, flashbacks fill in a difficult mother-daughter relationship. Mother (Maev Beaty) was a smart, free-spirited, Joni Mitchell-loving divorcee, who has clearly transmitted her resentments and anxieties to her daughter. Female identity and its construction from within and without are to the fore, albeit from a certain perspective: as one Cassandra points out to the other: “You’re a white, thin, middle-class, educated, hetero Canadian.” It’s directed by Patricia Rozema, who is possibly best known for her 1999 risk-taking adaptation of Mansfield Park; it doesn’t quite escape its roots in experimental theatre. The story occasionally verges on self-indulgent (or rather, selves-indulgent), but it is playful and ingenious.

• Mouthpiece is released on 12 March on digital platforms.