In an interview with IGN, Detective Pikachu Director Rob Letterman had this to say about the appearance of Pokemon in the upcoming movie:

“They’re incredibly real, you should think of it as the way [Marvel’s Guardians of the Galaxy character] Rocket Raccoon sits in the movie as if he’s really there. It’s that technology. The same group of people that worked on that, or worked on Jungle Book. We’ve got the people on it that worked on Fantastic Beasts. They’re technically, some of the most high-end visual effects in the world. It’s completely photorealistic, like they are alive and in the movie“