With that in mind, I thought it would be fun to do a little research to figure out the most popular dog breed in Maine. What is Maine's Most Popular Dog Breed? Because Maine’s most popular breed is the Labrador retriever. 1 pick, they actually led the nation, with 16 states having them as the most popular breed. However, finishing a close second was the Chihuahua, with 14 states having it as their most popular breed.