Road to the Multiverse is episode 01 of family guy season 08. It was originally aired on September 27, 2009.
Stewie and Brian travel through alternate universes. When They try to get back home, they run into problems and Stewie’s device keeps sending elsewhere. They find a universe where Dogs rule over people where Brian breaks the device. Dog-Stewie from that universe helps real Brian and Stewie get back home.