Fun brainstorming -- but it will never happen at DLP....
First, and foremost, the weather is only nice there for about three months each summer -- otherwise, it snows, its cold, the attraction blows water/mist across the audience, and it would be 100% misery, 0% enjoyment for most of the year.
Second, there really isn't anywhere they could currently do it without completely building a new lagoon/pond for it. They could do it, but the parks can't afford anything major like that.
Third -- and this is where the brainstorming has to go if you are serious about it: DLP only has Internationally Recognizable characters -- that means, you can't have any characters in a show that audiences of multiple languages wouldn't instantly recognize...not every Disney movie has been translated into French, Italian, German, Spanish (although most biggies have of course)...They would have ZERO idea of who Brother Brer is, for example -- although Lion King is very popular overseas....
BUT -- and this is a big but --
Fourth -- DLP is designed in such a way that many of its guests, even those staying in the resorts, go into Paris at night rather than hanging out in the parks or Disney Village. A nighttime attraction like Fantasmic would be three quarters empty every night. Also: there is a noise ordinance in Marne le Vallee which means they can not have any types of fireworks or loud noises after a certain hour (it used to be 8 pm although might have changed)...can't imagine a Fantasmic without a great sound system and fire effect.