Within EPCOT, I think Bistro de Paris has the most romantic setting for a couple.
San Angel Inn is another one that you might find romantic if you like more authentic Mexican food. But Bistro is elegant while San Angel Inn is not. San Angel is also louder and more bustling. Really the only aspects of it that are romantic are that it's VERY dark and that the "river and volcano" serve as backdrops. Most of us in our family love it anyway.
But Bistro gets my vote.