The nerves are making themselves heard through the PA at Jason Reitman's read-through of American Beauty. We're a couple of minutes into the director's re-enactment of Alan Ball's Oscar-winning screenplay, and a ghostly thrub-thrub, thrub-thrub is coming from the speakers in a packed-out Ryerson theatre in downtown Toronto. Reitman asks for each of his assembled cast's mics to be looked over, which means turning down Christina Hendricks, then cutting out Bryan Cranston. Nobody's checked it's not the actors' hearts that are thumping out across the 1,250-seat venue. They certainly look nervous enough.

Reitman's project seems a daunting task, even for established actors. His idea – to have stars such as Mad Men regular Hendricks and Breaking Bad's Cranston perform a classic film script on stage, for one night, live with no rehearsal – reveals a part of film-making that we rarely see: the learning process. A famous actor finding their way with a new script. Mistakes are expected, lines will be fluffed. It's a strange sensation seeing these people screw up – we're grown so used to seeing them edited perfectly.

American Beauty, a story about a middle-aged father who rejects the schlubby role he's been cast in, is a great fit for the series. Cranston – Hollywood's go-to guy for put-upon patriarchs – plays Lester Burnham rough and ready, with less of the acidity that won Kevin Spacey his Oscar. He is a touch more sleazy than Spacey, a bit more goofy, happy to yuk it up for the crowd. In the scene where Lester is caught masturbating in bed by his wife Carolyn (played here by Hendricks and by Annette Bening in the movie) Cranston uses a water bottle as an illustrative prop. Hendricks too gets in on some of the seedier farce. Her fake orgasm (in the scene in which Carolyn steams up a motel room with real estate king Buddy Kane) is a real roof shaker.

The supporting cast, unencumbered by roles that are hard to separate from Spacey and Bening, have more room to experiment. Arrested Development star Mae Whitman plays Lester and Carolyn's teenage daughter Jane petulant, which works perfectly with Girls actor Adam Driver's less creepy take on pot-dealing, bag-loving boy next door, Ricky Fitts. Sarah Gadon, who starred alongside Robert Pattinson in Cosmopolis, is great in the Mena Suvari role – the best friend of Jane who's coquettishness prompts Lester to start his life laundry. George Stroumboulopoulos, a Canadian TV and radio host, was a bit outpaced, but in this atmosphere – very actors' workshop, very "Yes and …" – it hardly mattered.

We're encouraged to think of movie stars as modern gods – flawless in speech, faultless in action, sexy geniuses, drilled to perfection on screen and in the public eye. It's in taking us behind that conceit that Reitman's idea really shines. The mistakes – the swallowed lines and the missed cues – brought this event alive. That's nothing to be scared of.