Not a dog...but had many of those wonderful traits.
Yeah, I had my ex-girlfriend's cat for several years after she left, and he exhibited many traits of a dog. He would often stand guard at the front door with my rottweiler and scare off the uninvited with snarls and the gnashing of teeth. He would sit at my feet just like a dog would, so I had Nelson my rottweiler on on side and Frog the cat on the other. They were the best of friends as well as partners in crime together.
I also trained Nelson not to touch his food until I had given him certain commands. This was to prevent him being baited, and strangely enough, Frog began doing the same thing.... wouldn't touch his food until I gave those same commands. Yeah, Frog may have been a cat but he behaved very much like a dog a lot of the time. Sadly, I have neither of them anymore, though it was over 20 years ago when the pair of them were scaring away and terrorising salesmen, Mormons and Jehovah's Witnesses.