One Piece has recently flirted more towards making movies kinda sorta canon. Strong World is basically intended to be canon but still self-contained so that you can freely ignore it if you only read the manga or whatever. Because of this, Oda had to state outright that Film Z was not canon.
Naruto's new movie is canon, too, as far as I know.
Strong World cannot be canon because of when it happened.
It's a lot like the first DBZ movie though that it wouldn't take much to make it canon.