The Four Seasons frontman, who turns 79 May 3, will play a club owner in the story about a self-centered, eccentric real estate agent whose life is turned upside down when his estranged son drops off a granddaughter he never knew he had.
The realtor, played by Douglas, eventually learns -- with the help of a determined, lovable neighbor played by Keaton -- to care and, to his surprise, fall in love again.
"When Harry Met Sally ..." director Rob Reiner is to direct "And So It Goes." Reiner's most recent film is "The Magic of Belle Isle."
Mark Andrus, whose credits include "As Good as It Gets" and "Divine Secrets of the Ya-Ya Sisterhood," wrote the "And So It Goes" screenplay.