In general, no, journals cannot arbitrarily share your submission with others—at least not before it's been accepted.
However, they can share your submission with:
- Reviewers, so that the peer-review process can be completed
- Other staff members within the publisher, which can be useful when a paper is submitted to the "wrong" section of a journal, or to the wrong journal, but is otherwise acceptable for publication.
Once the paper has been accepted and appropriate copyrights assigned, though, they can do more or less whatever they normally do in their publication and advertising process.