Is ONE PIECE episode 146 filler?
Canon No, episode 146 of ONE PIECE is canon.
#146
Quit Dreaming! Mock Town, the Town of Ridicule!
夢を見るな！嘲りの街モックタウン！
Aired 23 Feb 2003
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.