Is ONE PIECE episode 597 filler?
Canon No, episode 597 of ONE PIECE is canon.
#597
An Intense Battle! Caesar Exercises His True Power!
大激戦 シーザー真の能力発動！
Aired 26 May 2013
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.