Hi Rino:
Remy and Ratatouille are favorites of my family as well. While Remy used to perform six days a week, four times a day for guests at Les Chefs de France in Epcot, he's recently moved on. I'm hoping it's to make a sequel to Ratatouille and that we'll see him again at Disney World shortly.
Remy used to make an appearance in the Pixar Pals Countdown to Fun Parade at Hollywood Studios, but the parade stopped performances in 2013.
I miss Remy. C'est la vie. Some good news is that a
Ratatouille-Themed attraction is set to open in Disneyland Paris this year. I hope the attraction gets to the U.S. one day. You can also sail aboard the Disney Fantasy cruise ship and dine in their wonderful adult-only restaurant, Remy, where you can spot hidden Remys throughout the restaurant.
Except for the above, I've never been lucky enough to see a Remy character meet and greet in the Parks. But you never know. I would check with guest relations at any of the theme parks and ask them to call the "character hotline" for you. The character hotline will be able to tell you if, where, and when any particular character will be in the Parks that day.
Enjoy your vacation.