Eh, I think the Red Hair Pirates will be the main antagonist/rival in this movie.
No. The film is going to cover canon information of Shanks that Oda is scrapping from the manga.
Oda initially refused a Shanks movie (despite it being proposed to him several times) because he wanted to include it in the manga:
And yet he finally relented and decided to go with the movie. So it sounds to me like he scrapped some of Shanks' manga plot from the manga and decided to show that off in a movie.
To be very honest, this makes me update against Shanks playing an antagonistic or villainous role in the manga itself (why cover it in a movie if you're going to show it off in the manga).
If Shanks is an antagonist/rival or villain in this movie, he would almost certainly not be one in the manga.