Is it possible to create a metacourse that spans across an mnet?
Please elaborate. In the Moodleverse, the term "metacourse" has a special meaning - see the Metacourse doc page. Is that what you mean? However the answer will be probably negative. MNet is primarily an SSO solution for Moodle so that users from one site can roam to another site.
Not that I am aware of, but I would like to do this too. We have some departments that are bicollege, and have too identical classes, one at each school.
I believe we will manually create a course for the would-be metacourse -- rigging up something for the enrollments from the would be child at the other institution.
If you come up with a better solution, let me know.