I'd say maybe using models similar in style to Pokken Tournament, still cartoony but high quality textures for fur, hair, scales, skin, etc..
Because the thing is, you can't make a Pokemon not look cartoony without it becoming unrecognizable or ugly. Better to let them remain cartoony but with high quality textures and the animators making sure to apply believable physics (like making Pokemon feel like they have weight to them when running/jumping and have impact when they hit something or are landing from a fall). Would it look fake? Yes, yes it will, because Pokemon are creatures that can't naturally exist. So let Pokemon exist in their own way, don't try to force realistic textures onto them cause it'll just look ugly and no one would want it. It's going to have to be something that suspension of disbelief handles, as long as the writers and animators make it act like a living creature and have a natural personality it'll be accepted to exist within the movie's universe.
