Guillaume the conqueror

Why not? He thumbs his scrubby Gallic goatee thoughtfully. 'I'm quite preserved.' He means, surely, reserved. 'I don't go easily to people. I'm' Grumpy? 'Sometimes' Self protective? 'For sure.' Arrogant? Gifted? Deeply French? 'I think I'm a nice person, but I don't know if it's shyness or what but I like to be on my own. I'm kind of like a bear.' He makes a little clawing motion with his hands, and gives a half-hearted snarl.

As well as his ursine qualities, there was another reason Guillaume and Marion didn't get together earlier: he was married to the actress Diane Kruger. Meeting in Paris as drama students in 1999, they wed in 2001 and worked together on a film he directed, Mon Idole (a reality TV satire), before splitting amicably, citing work pressures, in 2006. She even appears in Canet's latest film Farewell as 'woman jogger', a blink-and-you'll-miss-her cameo, made out of loyalty to its director, Christian Carion, who directed them both in the First World War film Joyeux Noël. 'Yeah, we stayed really good friends. She's a great woman, sure,' he says, eyes wandering round the room.

He never meant to be an actor but a showjumper. Born in the southwestern Paris suburb of Boulogne-Billancourt, the only son in a family of horse-breeders, he grew up in the rural district of Rambouillet and was a member of the Junior French National Equestrian team. 'I was on my way to be a professional horse rider until the accident,' he says. 'I was broken all down my right side. I did not have to stay in bed a long time, but I realised I had spent all my youth being in horse competitions, seeing the same people all the time. I was 18, I wanted some new things.'

So he started making short movies on Super 8 film and enrolled at the prestigious Cours Florent drama school as an actor. 'I went because I wanted to understand how to direct actors,' he stresses. In 2003 he directed his first full-length feature, Mon Idole, in which he also reluctantly starred. 'I was not supposed to, I preferred to be behind the camera but the actor left at the last minute, so finally I did it.'

He likes to project a fearless image. 'I have done many sports for a long time. I did motorcross racing, I did horse competition, I did martial arts, I 'ave done boxing for four years.' Does anything frighten him? 'Not really,' he says, a smile emerging from his goatee. 'I like adrenaline.' But wasn't boxing a bit reckless given your, you know, très beau visage? Think of your fans! 'Yes,' he acknowledges. 'That's why I stopped.'

When he directed Tell No One, he invented a small part for himself (which did not feature in the original Harlan Coben novel) as a showjumping champion, charging triumphantly around the paddock in what must have been a wonderfully wish-fulfilling scene. His character then went on to beat up an innocent woman and take part in a homicide plot. The film was nominated for nine César awards, and carried off four, including Best Director. Kristin Scott Thomas in a supporting role helped it win an audience in the UK.

But it was on the arm of his girlfriend that Canet attended the Oscars. In 2008 Marion Cotillard was nominated for Best Actress as Edith Piaf in La Vie en Rose. He went along, finding LA 'interesting, sometimes nice, not somewhere I want to be all the time'. In winning the award, Marion became the second woman in Canet's life to enjoy a huge career boost. Three years into their marriage, Diane Kruger had become, officially, the most beautiful woman in the world when she was cast as Helen of Troy in the Hollywood epic Troy. Now Cotillard's career was shifting gears before his eyes. Is it hard being with being someone whose life changes in such a dramatic way? 'It's not a dramatic way, it's just a good way,' he says firmly. 'No, I'm very proud of her and I'm very happy for her, because I've known Marion a really long time, we've been friends for a long time also.' Is he good at being supportive? 'For sure. I'm her biggest fan.'

That said, I can't imagine him doing the washing-up, nor does it sound like he cooks much. 'I like good food, but I'm not very patient. If I have to, or if I'm alone, I'm cooking. But usually I let the other one do it.' By 'the other one' he could mean Marion or a domestic helper, I'm not quite sure which, but when I press him, he manages to remember cooking parmesan and shrimp risotto or omelette with Iberian ham.

It sounds as if he takes up quite a lot of room in their Paris apartment in the Marais with his guitars. He loves to play and has a mix of electric and acoustic instruments, as well as a vintage collection, because 'they're even better when they're old, like good wine'. His favourite one is signed by Robbie Robertson of The Band, a long-time hero turned acquaintance. Like any self-respecting French artiste, Guillaume Canet is working on an album full of melodies. His flat is crammed with film DVDs, too, of course. 'Because I'm cynical and sarcastic, I like English humour.' Such as? 'Montee Peeton!' he cries. I realise he means Monty Python.

His latest project, which he has written, acted in and directed, is Les Petits Mouchoirs, which translates in my schoolgirl French as 'The Small Handkerchiefs' but is, in fact, an idiom for 'Little White Lies'. It's an ensemble piece similar in structure, he says, to the college reunion film The Big Chill (1983, starring Glenn Close and Jeff Goldblum) and, he adds with a proud smile, Marion Cotillard is one of the leads. But first he has Farewell in cinemas, a gripping tale of Cold War espionage in which his accidentally heroic character (he is only acting this time, not directing) called for him to hide his smouldering eyes behind a pair of spectacles.

'It was an idea of mine after I talked to the director. I wanted to look like someone really intellectual. I liked the idea of a hero who doesn't look like a hero – like Richard Dreyfuss in Jaws. And it helps you to go into the character when you have some accessories.' A true story that is already reigniting old controversies, it was banned from being filmed in Moscow, even though it's anti-Soviet rather than anti-Russian. 'Well, you know, Putin is an ex-commandant from the KGB so they don't want to talk about all this. The subject is still really powerful.'

Guillaume has just filmed Last Night in New York with Keira Knightley. 'She's really great, she's an amazing actress and as a human being she's really smart, really on her feet – you know this French expression?' I'm guessing he means 'grounded'. 'I never saw any starification. Sometimes it was difficult for her because we were shooting in the street and there are like 40 paparazzi and we can hear their cameras going tick tick tick tick tick tick tick tick'