The description for OUAT's version of this character is that he's a "handsome, hearty, salt-of-the-earth" guy whose "sometimes-gruff demeanor...can hide his deep love for Anna and her sister Elsa. When we first meet Kristoff on Once, he is adjusting to life at the castle — including sleeping indoors for the first time in his life." It sounds like the actor will need comedy chops, and apparently OUAT's version of Elsa will be in her late 20s or early 30s, so we expect Anna and Kristoff to be in their 20s.
With that in mind, here are five actors we could see rocking this role.
Why switch it up at all? Jonathan Groff was perfect as the voice of Kristoff, and his age and looks would work for the live action version, too. Sure, he'd need to dye his hair, but we can see him as a blonde.