Canadian Howard's work visa was not approved, according to a spokesperson for the New Jersey venue.
McGowan was previously seen at the Paper Mill in Kiss Me, Kate (Fred/Petruchio) and Master Class (Tony). His Broadway credits include Ragtime, Grease, The Apple Tree, Priscilla and The Producers.
Directed by Rob Ruggiero and choreographed by Ralph Perkins, performances will continue through May 4.
Leading the cast are Erin Mackey as Ensign Nellie Forbush, Tony Award nominee Loretta Ables Sayre as Bloody Mary, Tally Sessions as Luther Billis, Doug Carpenter as Lt. Joe Cable and Jessica Wu as Liat.
Rounding out the ensemble are Andrés Acosta, Faye Bautista, Grady McLeod Bowman, Will Burton, Meggie Cansler, Matt Faucher, Joanne Javien, Caitlin Maloney, Christian Marriner, George Merrick, Brian Ogilvie, Samantha Joy Pearlman, Michael Scirrotto, Paige Sommerer, Ryan Steer, Jeff Sullivan, Teddy Tinson, Grace Wales and Gregory Williams.
Adapted from the Pulitzer Prize-winning novel "Tales of the South Pacific" by James A. Michener, South Pacific, according to press notes, "is an exquisite story of romance and love set against the backdrop of a lush tropical island during World War II."
The creative team also includes scenic designer Michael Yeargan, costume designer Catherine Zuber, lighting designer John Lasiter, sound designer Randy Hansen, costume coordinator and additional designer Leon Dobkowski, hair and wig designer Leah J. Loukas and production stage manager Gary Mickelson.
Tickets may be purchased by calling (973) 376-4343, at the Paper Mill Playhouse Box Office at 22 Brookside Drive in Millburn, or online at www.papermill.org.