Board Thread:Naruto Discussions/@comment-4271790-20140806084414/@comment-1512913-20140809130259

Not absolutely. The filler was an adaptation of canonical events, meaning the general plot details are canon, like Kakashi becoming an ANBU, Itachi massacring his clan etc. But the rest, like smoke people, exact missions of Kakashi as ANBU and his interaction with people, his depression, the way he and Yamato met etc. are unlikely to be truly canon. The author most likely envisioned them differently and the way it's shown in the anime is just their educated guess about how they think the little details played out.