What Dog breed was Dreyfus?

There is a website that answers your very question.

The link is: http://emptynestonline.net/show_info/frequently_asked_questions.

It states:

Frequently Asked Questions

Question 1: What is the real name of the dog who played Dreyfuss?

Answer: Dreyfuss was mostly played by a dog named Bear. However, Bear's brother Julio occasionally stood in as Dreyfuss.

Question 2: What breed of dog is Dreyfuss?

Answer: Bear's father was a Golden Retriever mix, and his mother, a St. Bernard. For more information about Bear's breeding, check out our "Return to the Nest" interview with his trainer, Joel Silverman. (Link here: http://emptynestonline.net/return_to_the_nest/joel_silverman.)

There is a lot of interesting information about Dreyfuss (Bear) at that link provided in Question 2 above.