Is Bleach episode 366 filler?
Canon No, episode 366 of Bleach is canon.
#366
Changing History, Unchanging Heart
変わりゆく歴史、変わらぬ心
Aired 27 Mar 2012
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.
No canon episode follows this one yet.