No. Anthropomorphic/Sentient/Talking animals don't, in and of themselves, make a film/book/TV programme/comic into a fantasy if the central conceit is that talking animals do already exist within that fictional universe. Stuart Little would be an excellent example of this.
That said, we would consider talking animals to be part of a fantasy if:
They had been uplifted in some way (either by technology or magic)
Their speaking was somehow fantastical to the other characters.
The talking rats in Ratatouille would certainly fall into the latter category. There's no specific evidence of how they became intelligent but it's clear from the scenes in the film that animal sentience certainly isn't a normal feature of that universe.
LINGUINI : I need this job. I’ve lost so many. I don’t know how to cook and now I’m talking to a rat as if you actually understand what I’m say--
(sudden realization)
--did you NOD?? You UNDERSTAND ME??
