Hi, Ghislain! Sounds like a fun evening. The only way you'd be able to see Wishes or Illuminations from Downtown Disney would be timing it just right for
Characters in Flight, which takes you 400 feet above Downtown Disney for a panoramic view over the entire Walt Disney World resort. You would be able to see the nighttime spectaculars this high in the air; however, timing it just right might be tricky.
Alternatively, you could grab a cab outside of La Nouba and go to the Polynesian, where you can watch Wishes from the beach. I think you wouldn't be able to get to Epcot in time for Illuminations.
On the Polynesian resort's beach, the Wishes music and narration is piped in through speakers to enhance the experience. If you have time to spare before the 10:00 p.m. show, take a quick detour when you arrive at the Polynesia and go to Captain Cook's to grab a DOLE-WHIP to enjoy during the show.