Is ONE PIECE episode 285 filler?
Canon No, episode 285 of ONE PIECE is canon.
#285
Obtain the 5 Keys! The Straw Hat Pirates vs. CP9!
５つの鍵を奪え! 麦わら一味対ＣＰ９
Aired 12 Nov 2006
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.