Is ONE PIECE episode 277 filler?
Canon No, episode 277 of ONE PIECE is canon.
#277
The Tragedy of Ohara! The Terror of the Buster Call!
オハラの悲劇！バスターコールの恐怖
Aired 24 Sept 2006
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.