Personally, I can't think of a single place in Epcot that is not a good fit for a 3 year old. The ones that I find least attractive for a kid that age are (in no particular order):
CS at the American Pavillion--As an aside, I think this place is a complete embarassment given the effort and theming that the other countries bring to the table, pun intended. Even if you are wedded to the idea of serving burgers and fries, at least dress the place up like a 50's diner or give it some other Americana theming, like maybe Rte 66.
Le Cellier--A bit dark to catch the attention of a 3 year old.
Morroco--Might be menu issues for a 3 year old.
Rose and Crown--A bit loud and "pubby" for a kid.
Other than that, I think my kid enjoyed pretty much every single place we ate at Epcot when she was between 2 and 5, which includes pretty much every single Epcot restaurant. And she was never a "kid's menu" type of kid. Always wanted to try the adult food.