Rivera starred as Collette in the first two seasons of the Step Up series, which aired on YouTube before moving to Starz. Production on the new season started in February in Atlanta.
Step Up is based on dance-focused film series of the same name. Rivera died at the age of 33 in July from accidental drowning while boating with her 5-year-old son Josey.
"I am so excited to join the Step Up family. I know I have massive shoes to fill. Naya was incredible. I hope to honor Naya, her family, friends and fans with a great performance," Milian said in a statement.
Step Up follows Collette and Sage Odom, portrayed by Ne-Yo. Sage is the founder of Atlanta's High Water Performing Art School with Collette as his partner in art, business and love. Collette became the manager of Sage and his tour, while hiding a dark secret. Collette, as the secret comes crashing down, is tempted to change from her role as the woman behind the man to the powerful woman in front of the man.
Faizon Love, Jade Chynoweth, Carlito Olivero, Terrence Green, Eric Graise, Kendra Oyesanya and Tricia Helfer also star.
"There is no replacing Naya. Let's get that straight. Her spirit lives on in our memories and every part what this show is and will be," Ne-Yo said in a statement.
"Christina has big shoes to fill and she knows it, which speaks to her poise and respect as a person and an artist. I'm more than certain of her ability to bring an energy and light to this character that Naya's fans as well as the rest of the world will love. We've welcomed Christina with absolute open arms and have rallied around her with love and support. I'm excited and can't wait for the world to see this!" he continued.
Holly Sorensen serves as creator and executive producer. Adam Shankman and Jennifer Gibgot, who produced the original Step Up films, are executive producing along with original stars Channing Tatum and Jenna Dewan.
The first two seasons of Step Up will be available on Starz across all platforms and will begin airing on the network every Friday at 8 p.m. EST starting on March 5.