Can a McGill students take courses at Concordia University in Montreal?

My son was admitted to McGill and he wants to study computer science. However, he has other interests too, such as comedy writing, creative writing and theatre. His one hesitation about attending McGill is the lack of courses in the creative arts.

For those who are familiar with McGill and/or Concordia, are McGill students able to take courses at Concordia, and will they transfer in as electives if McGill does not offer a similar course?

My son would be an international student. I don’t know if this would make a difference. Thanks!