Vaporeon's origins are uncertain, though it could be based on a cross between cetaceans, felines, and canids. Its feline and fish characteristics may mean that Vaporeon may be a visual pun on the catfish. The fins and dorsal lining may be based off different types of tropical fish. Its ears resemble a mix between a fish's fin and a fennec fox's or caracal's ears. It also shares characteristics with mermaids. Vaporeon may also be inspired by the Telchines of Greek mythology, or the Merlion, a national symbol of Singapore. Vaporeon's resemblance to both carnivorans and cetaceans could be based on primitive whales, such as Kutchicetus.
Vaporeon - Bulbapedia
From what the passage says, Vaporeon is something like a combination between a lot of things.
However, I think Vaporeon is more cat than dog, to answer your question. After all, it has feline characteristics.
Err, hope this answered your question ^^'