I stumbled over a tweet from Margaret Atwood in my feed yesterday, pointing me to the literary magazine Matrix Magazine. I had a look and it sounds quite cool. They've been around since 1975, so quite well establishde:
Matrix Magazine is a literary magazine with an ecclectic, quirky character, and a thirst for innovation that can't be satisfied. We try, though--we try. And we keep our submission base open to many art forms, including all manner of literary work—poetry, fiction, nonfiction, interviews, essays, humour writing, columns, reviews, and other experiments—as well as illustration, comics, photography, and anything else that can be represented in print.
Matrix has a regular themed 'Dossier' section, which is where guest editors make calls for themed submissions. At time-of-posting this isn't open, but if you keep an eye on the About page, open submission calls will appear in their 'Submissions' section.
Check out the home page here: http://www.matrixmagazine.org/