I've always pronounced it Mad-uh-lin, with a -lynn ending. But I've never known anyone named
Madeline, so I don't know how bearers themselves pronounce the name.
Except, when I used to read the book "
Madeline" to my daughter, I pronounced the last syllable just like the word "line", because otherwise it wouldn't have rhymed the way it was supposed to. But I had to make an effort to do it.