Burns, who stood by for Idina Menzel in the Broadway production of If/Then, assumes the role of Liz/Beth, with Gray ("American Idol," Rent) and Hydzik (Side Show, West Side Story), taking over the roles of Kate and Josh, respectively.
They succeed LaChanze and James Snyder, the show's original cast members, who launched the tour with Menzel.
Remaining with the tour from the Broadway production is original star Anthony Rapp, who will continue in the role of Lucas.
If/Then is the original musical that reunites composer Tom Kitt, book writer/lyricist Brian Yorkey and director Michael Greif, the creative team behind the Pulitzer Prize and Tony Award-winning musical Next to Normal.
The cast also features Janine DiVita as Anne and Daren A. Herbert as Stephen and Marc de la Cruz as David. The ensemble includes English Bernhardt, Charissa Bertels, Xavier Cano, Trey Ellett, Kyra Faith, Corey Greenan, Cliffton Hall, Deedee Magno Hall, Tyler McGee, Joseph Morales, Emily Rogers and Alicia Taylor Tomasko.
If/Then features choreography by Larry Keigwin, set design by Tony Award nominee Mark Wendland, costume design by Emily Rebholz, lighting design by Tony Award winner Kenneth Posner and sound design by Tony Award winner Brian Ronan.
The tour began performances Oct. 13 in Denver.
According to producers, "If/Then is a contemporary new musical that follows two distinct storylines in the life of Elizabeth, a city planner who moves back to New York to restart her life in this city of infinite possibilities. When her carefully designed plans collide with the whims of fate, Elizabeth's life splits into two parallel paths. If/Then follows both stories simultaneously as this modern woman faces the intersection of choice and chance."