The actor had already signed up to serve as producer on the film, which is Ryan's directorial debut.
As well as his work behind the camera, Hanks is now in talks to make a cameo appearance, according to The Hollywood Reporter.
Set in a small Californian town in 1942, the film follows a 14-year-old called Homer Macauley, who is deemed the best and fastest bicycle telegraph messenger in history.
When his older brother goes to war, he is left to look after his widowed mother, his older sister and his 4-year-old brother, and to bring hope to their community.
Ryan is due to play the character's mother, while Sam Shepard, Melanie Griffith and Jack Quaid will also feature in the movie.
The pair have appeared on screen together in three films throughout their careers, including Joe Versus the Volcano and You've Got Mail.
Ithaca is an adaptation of William Saroyan's 1943 novel The Human Comedy and begins shooting in Virginia next month.