Watashi no inu wa Chūbakka no you da.
Chūbakka mitai da.
Chūbakka ni niteiru.
Chūbakka ni mieru.
Furthermore, you can't use "~sou da" to describe appearance of what you really see, even when used with adjectives. For instance, you can say "kashiko sou desu (looks like clever)" when you see a dog, but you can't say "ooki sou desu (looks like big)" or "kuro sou desu (looks like black)". ("Kuro" is the stem of an adjective "kuroi", not a noun, in this case.)