Cannes can always do worse than choose a comedy for its opening gala, and the festival is off to an amiable, entertaining start. Quentin Dupieux brings the wackiness onstream with this cheerfully mischievous, unrepentantly facetious fourth-wall-badgering sketch. It’s a sprightly meta gag, a movie about a movie, or perhaps a movie about a movie about a movie – or perhaps just a movie, full stop, whose point is to claim that reality as we experience it inside and outside the cinema is unitary despite the levels of imposture and role-play we bring to it. It is all just one unbroken skein of experience like the endless dolly-track (the temporary rail that lets the camera move smoothly) that Dupieux finally shows us.

There are plenty of laugh lines, though The Second Act would be a bit thin were it not for the rich, creamy thickness of the alpha-grade French acting talent involved. We see a nervy, unhappy guy called Stéphane (Manuel Guillot) open up his restaurant in the middle of nowhere, quibblingly called The Second Act. Two young men are seen walking towards the restaurant: David (Louis Garrel) and his pal Willy (Raphaël Quenard, from Dupieux’s previous film Yannick). David has a date there with a beautiful woman, whose clinginess and neediness he nonetheless finds a turnoff, so he’s brought Willy along to seduce her and take her off his hands. This woman, Florence (Léa Seydoux) is preparing to meet David, unaware of his plans to palm her off on someone else, and so confident is she that David is the One that she has actually brought her dad with her, Guillaume, played by Vincent Lindon.

The actors playing these parts keep breaking out of character, and quarrelling among themselves – though without anyone saying “Cut!” The action moves seamlessly in and out of the apparent levels of fiction and reality, perhaps as a result of the novel way it appears to be directed – by AI, a robotic voice from an avatar on a laptop held up by a lowly runner.

Dupieux naughtily pokes fun at the progressive scruples of the film industry; one character appears homophobic and transphobic until the film tips us the wink that this is just an illusion. Or is it? The Second Act even takes the mickey – on the same provisional, inauthentic basis – out of #MeToo activism, a subject the industry takes very seriously indeed. And yet Dupieux also does lots of gags about sad losers taking their own lives by shooting themselves; now, some might find this as uncomfortable and contentious as anything else, although it is presented as quite separate from the self-aware jokes about silly liberal wokery.

The Second Act is an odd film in some ways. For all its knowing and arch attitude, it is weirdly unsophisticated and even undemanding, more undemanding than Dupieux’s previous comedies such as Smoking Causes Coughing and Incredible But True. There is no real tension or revelation in the discrepancy between true and false, and the actors are not supposed to actually be Garrel, Seydoux etc as they would be if they were appearing in, say, an episode of Larry David’s Curb Your Enthusiasm. And yet Guillaume is over the moon about a job offer from a real-life director: Paul Thomas Anderson lui-même.

The running comic theme of The Second Act is that there is something basically very silly about acting in films; pretending to be made-up people in made-up stories when there are important things going on in the world which need grownup people doing proper jobs. Florence’s mother is a surgeon and is candidly unimpressed by her daughter’s career – but Florence is convinced that actors’ work is valid, like the magnificent heroism of the musicians on the Titanic who continued to play as the ship sank, to calm and comfort the passengers. Guillaume contemptuously laughs that this is just an urban myth, a fiction invented by James Cameron, and only naive idiots believe it. It’s an amusing piece of mischief on Dupieux’s part, designed to get people Googling the Titanic musicians after the film is over. Perhaps there is nothing much to The Second Act, but the soufflé of self-awareness rises tastily enough.

• The Second Act screened at the Cannes film festival.