Is ONE PIECE episode 413 filler?
Canon No, episode 413 of ONE PIECE is canon.
#413
A Difficult Fight for Luffy! The Snake Sisters' Haki Power!!
ルフィ第苦戦！ヘビ姉妹の覇気の力！！
Aired 16 Aug 2009
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.