Now that you’ve gotten some responses and had a chance to think let me elaborate!
Shula’s is a legit steakhouse. The service is excellent, the aged angus beef is top notch, the seafood is equally good (seared ahi tuna, to die for), and the desserts are great. It has everything you want from a high end steakhouse, and as steakhouse prices go it’s not cheap but it’s better than Morton’s! What it doesn’t have (and this has been my wife’s knock on the Swan/Dolphin in general) is any Disney atmosphere. At the hotel, in the restaurant...you could be anywhere. That never really bothers me, but my wife isn’t crazy about that. The last consideration is when you are going and where you will be. If you are in Epcot it’s a nice walk out the International Gateway over to the Swan/Dolphin. You can go past the Yacht/Beach or along the Boardwalk and you’d want to give yourselves maybe 15 minutes at a leisurely pace. The walk could be less pleasant in the summer heat. We ALWAYS have great meals at Shula’s and leave wanting to go back again.
Le Cellier is a different animal, but a great choice in its own right. It’s not so much a true steakhouse, but a great restaurant that features very good steaks. Yes, it is a little “dark” (it is a cellar, after all!) and can be a little noisy (all those Canadian servers telling the stories of their provinces adds to the din), but for us that is all part of the charm. After all, we are in Disney and this makes us feel a part of Canada, some of the Disney atmosphere that sets the parks (and resorts) apart! We’ve eaten there a lot and never been disappointed by a steak (although they did fail to render the fat properly on the duck breast last go around, but didn’t charge us for the entree), and the rest of the menu is very good. The pretzel bread is the best bread on the planet, dipped in cheddar cheese soup it’s even better. Desserts are very good, too. Our service is always excellent.
No idea when you are going or at what hour you like to eat, but as a date night goes I’d try this if you opt for Le Cellier. Make a late reservation, like 8:15ish, when Illuminations is at 9:00. We’ve done this a few times. That will give you time to order and have a drink and appetizers before Illuminations starts. Let your server know when you are ordering that you’d like to step out for the show. Just before 9 head out and catch Illuminations. We like to view from the steps leading up to the Canada stores. After the show come back in and finish your entrees, dessert and coffee. When you are finished the park will be closed and mostly emptied out. From Canada take a nice, long stroll around World Showcase Lagoon. If you are headed for the front of the park walk toward England and go around that way. If you are headed for International Gateway head toward Mexico and around that way. With the low lights, no crowds and music playing it’s a pretty magical walk (if you are up for walking at that point) and would be a romantic end to a nice date night!