I imagine that Film RED will fall into that sort of quasi-canon status that every movie since Strong World has more or less fallen into.
Strong World is more special than its subsequent movies. 1- Oda was actually credited as main writer on SW, not just as a creative supervisor like in the rest. 2- Shiki and Indigo are confirmed canon characters while neither the characters created for the other movies nor their backstories were confirmed canon. 3- Oda released a special canon chapter (chapter 0) in shonen jump for Strong World which didn't happen with the other movies.
So this brings the question of how similar Red will be to SW in the aforementioned aspects or if it will receive the Z/Gold/Stampede treatement instead.