Ali Wong and Randall Park said that Keanu Reeves was their first choice for the film. The script was sent to him, but Wong and Park never thought they would get him. However, Reeves had watched Wong's Netflix special Ali Wong: Baby Cobra (2016) and said yes. Wong said he wrote "I would be honored to be part of your love story." Park said that Reeves was quoting lines from Wong's special.
Keanu Reeves filmed all his scenes in 4 days between shooting John Wick: Chapter 3 - Parabellum (2019). All of his scenes were filmed in San Francisco instead of Vancouver, to accommodate his schedule.
During an interview on the National Public Radio program "Weekend Edition Sunday," Ali Wong said that one way she wanted to set this movie apart from other, more conventional romantic comedies was to omit the traditional "makeover" subplot for the female lead: "Something that people picked up on is that she wears her glasses from the beginning to the end, which is extremely rare in a rom-com. Usually, there's some sort of makeover, where they ditch the glasses. And I'm not ditching those glasses."
Keanu Reeves improvised some of his scenes. It was his idea to list all of the Chinese dignitaries in the game night scene. Reeves also improvised the lines "I missed your light"/"I missed your soul", and "I don't have a problem, Sasha. What's your problem?" along with the karate gestures.
Ali Wong told New York Magazine that when it looked like Keanu Reeves might not have been available, a number of other men were considered for his role, including Hong Kong actor Tony Leung, Filipino-American actor and martial artist Mark Dacascos, Indian-American director M. Night Shyamalan, and Paul Giamatti (not Asian). The last option was Randall Park's idea (he thought Giamatti would be a funny choice) but Wong vetoed it, explaining, "It was very important to me that it be someone who was Asian-American who would also be Marcus's worst nightmare. Because if Daniel Dae Kim [who plays Sasha's fiancé in the beginning of the film] showed up, you'd be like, 'Ahh!' if you were Marcus. It's got to be even worse than that. So it's got to be someone who's internationally iconic, and someone who fits those two Venn diagrams is basically Keanu Reeves.... It's always been important to me, to express my desire and attraction toward Asian American men. Since I first watched Speed, I was very aware that Keanu was Asian American because my family and community wouldn't shut up about it. Maybe other people didn't know but I never forgot that."