It is actually pianist Pierre-Yves Plat's hands that can be seen in the opening credits sequence, not Gad Elmaleh's.
Both Sacha and Charlotte's apartments were actually built in a studio. Director James Huth claims that this was to give the film some glamor and make it look like an American comedy from the fifties, having been inspired by directors such as Billy Wilder, Frank Capra and George Cukor.
The New York scenes were initially set in Montréal, Canada in the screenplay. The setting was changed at producer Richard Grandpierre's insistence, who also decreed that it should rain during the first scene.
The role of Sacha's grandmother is played by James Huth's own 94 year old great aunt. Despite speaking French, her lines are subtitled in the original release.
Several references are made to The Aristocats (1970) throughout the film and co-writer/director James Huth feels that one can view this film as a modern re-imagining of the Disney animated classic.