If a group of people perform a "show", they are referred to as "the cast".
Cast and crew is a common reference. The crew being the stage assistants, and so forth. They manage the lighting, costumes, and any other material needs.
"Showcast" is a bit awkward. Cast is more common.
It would be common to see a wording like this; "The show could not be played."
"Cast" would not be included in such a phrasing.