I know the original pronunciation of
Madeleine (mad-LEHN).
Madeline, on the other hand, I'm not as sure about. I would assume in French it would be mad-LEEN. I will tell you this. The wife of
Ludwig Bemelmans (author of
Madeline) was named
Madeleine, however, he chose the
Madeline spelling for his books. I've wondered if he used that spelling because it lended itself so easily to the many rhymes contained in the book (vines, lines, nine, shine). The books and movie have become so well known that I wonder if people would automatically assume it's pronounced mad-a-LINE so if that's the pronunciation you prefer, then you shouldn't have a problem. Still, I've known Madelines who've pronounced it mad-a-LYN.
I prefer the
Madeleine spelling because it's the original. It's the one I'd use, however, I can easily see that spelling and pronunciation becoming just as confusing. ;-) It's a pretty name no matter how it's spelled and pronounced.