As previously reported, the cast also includes Uma Thurman and Australian newcomer Jordana Beatty.
Vigneron Coudroy was selected from an extensive casting process in London and Paris. He plays the role of Jean-Luc, who befriends Eloise during a vacation in Paris.
The schoolboy has also appeared with Gerard Depardieu and Carole Bouquet in Nicolas Bary's Les Enfants de Timpelbach and has appeared as a dancer and performer in several theatrical productions in France.
Charles Shyer said: 'It's a rare to write a part and then have an actor come in and read it exactly the way you heard it in your mind. That's what happened with Marcus. Four words into his audition, I knew our search was over.'
Shyer co-wrote the script with his daughter Hallie Meyers-Shyer and Larry Spencer. Producers are Patrick Meehan, Thomas D. Adelman, and Ron Rotholz of HandMade Films. Shyer will also executive produce.
HandMade International is handling sales. The company's Cannes slate also includes 50 Dead Men Walking, The Long Good Friday, Cracks, and Last Battle Dreamer.