stopped by the “Today” show Monday where he revealed how he got cast as a merman in Greta Gerwig’s upcoming “Barbie” film. According to Cena, 46, the opportunity to be in the highly anticipated film came in the form of a chance encounter with “Barbie” actress Margot Robbie, 32, who was filming her movie across the street from his latest “Fast & Furious” installment. “It was a happy accident, and I think ‘Barbie’ and ‘Fast X’ share a lot of parallels,” Cena said during the “Today” interview.