This is one way Hollywood traditionally markets their films… they find at least two big stars, they pay them millions of dollars and they cast them in the film whether they are right for the story or not. They cast them because they assume that stars guarantee bums on seats whether the movie is good or not.
It’s good risk taking and lazy story telling.
Here is a new idea; instead of using stars to promote your film why not use your characters to promote your film. Do your characters have a life before the camera rolls? What if the audience got to see a little of that life?