The Eeveelutions are based off of foxes, which are in the Canidae family along with dogs. However, they share many traits with cats as well. Generally they have feline faces and and a canine physique.
So to answer your question, Glaceon is primarily based off of a fox, but shares features with both cats and dogs as well.
>Eevee shares traits with foxes, more specifically the fennec fox, dogs and cats.
[Source][1]
(this is a fennec fox btw)
![fox][2]
[2]:http://exoticanimalsforsale.net/img/fennecfox.jpg
[1]:http://bulbapedia.bulbagarden.net/wiki/Eevee_(Pokémon)#Trivia
