Board Thread:Theories and Speculation/@comment-1512913-20161119171442/@comment-25122992-20161207225142

Depends on what are you speaking about. Kakashi's clash with Edo-Zabuza/Haku + the rest of the Edo-Swordsmen is cannon, it's in the manga as well. Only the individual fights (Kakashi/Guy vs Jinpachi/Kushimaru; Kakashi/Lee/Sai vs Jinin; Omoi vs Ameyuri) are filler episodes, though I think these were nice fillers.