"I have broken all my bones, all my youth," Guillaume Canet says on a long summer day's drive out of Manhattan. In a bumpy town car with the windows down, the French actor-turned-acclaimed-director is about to talk to suburban cineastes about his new heartsick thriller, Tell No One, but in the meantime, he's recounting his bloody tumbles off horses and muddy spills as a motocross rider. Canet, 35, was raised by horse breeders, and as a teenage equestrian champ knew that every ride was a risk. In one competition, Canet and his horse Rimsky hit the ground together, and as Rimsky fought his way back up, his hooves on Canet, the rider rethought his life. There had been scarier falls — one sent him face-first into a wall — but the rough landings taught him humility. "You can be champion of the world," he says, "but the day your horse is sick, you're nothing."

In the 17 years since then, Canet has turned himself into something. As an internationally lauded actor — known best to Americans for The Beach — and the youngest director ever to win a César, he is learning to like casting more than being cast. He has always harbored an interest in calling the shots, and now throws himself into the action, often holding the camera himself. One scene in Tell No One hurtles the main character — a crumpled doctor chasing down clues about his wife's murder — across an eight-lane highway, and Canet followed him right into the oncoming traffic. Canet inserted himself in front of the camera too, playing the son of a Paris aristocrat who happens to be — bien sûr — an equestrian show jumper. He cast his own father as the doctor's père, and Marina Hands, the statuesque French actress whom he knew from the teenage equestrian circuit, as the doctor's sister.

Still, as much as he shares those close to him with audiences, Canet tries to shield his real-life relationship with Marion Cotillard from public view. They first appeared as lovers on film (in Jeux d'enfants), but as Canet had already worked with, married, and divorced the otherworldly Diane Kruger, he now knows better than to feed such interest. He didn't even attend Cotillard's big Oscar night last spring, though he was nearby in Los Angeles, staying out of her spotlight. "It was something personal, and I was happy for her and so proud of her," he says.

Though Canet splits his time between Paris and the French countryside, he relishes New York, especially when a visit there involves a three-hour gab session at Martin Scorsese's place, to name one recent highlight. Change energizes him, he says, pushes him past the comforts he should seek now that his injuries are catching up to him a bit. To keep things interesting, he picked up a Martin guitar six years ago and now never travels without it. "It's just a hobby," Canet says, but admits it's become a passion, made more intense because he feels no pressure to succeed. Not long ago he joined a musician friend — the French recording artist Mathieu Chédid, known simply as M — before 5,000 Lyonnais concertgoers. Says the man who's acted for both stage and screen, "When you try to have the balls to go on the stage — only you, with your guitar — that's something scary!" He allows, however, that if he and his friend had practiced more than one song, he would have been up for an encore.