Is Bleach episode 206 filler?
Canon No, episode 206 of Bleach is canon.
#206
The Past Chapter Begins! The Truth from 110 Years Ago
過去編開始！１１０年前の真実
Aired 10 Feb 2009
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.