Well...I know three is no "official" recognition of Walt's birthday...because I was in Disneyland on that day last year...and there was nothing special done (plus it was my birthday as well....so at least I had a b-day sticker)
So I'll say Mickey's, Disneyland's and WDW's are the 3 recognized B-Days....
My original answers of Mickey and Donald still stand. I will guess Snow White for the third. (My first inclinations was to say Goofy, so if it is Goofy instead, remember I said that first )