Real dogs are used in 95% of the film.
At first, Will Forte was hesitant to accept the role of "Doug" because he is an animal lover and didn't want to be portrayed as an animal abuser since it might potentially send the wrong impression of him as a person. However, he would later accept the role because he hates people who abuses animals and wanted to show that animal abusers deserve karma.
The film uses a mix of real dogs with a few shots of an animatronic one.
(at around 29 mins) Josh Gad is the voice of Gus, the Labrador Retriever who was narrating his owners story at the fair. Josh Gad was the voice of Bailey in A Dog's Purpose (2017) and A Dog's Journey (2019); in both movies, the dog narrates his owners story. And his owner in both movies is Dennis Quaid, who appears in this movie as himself who was bird watching.