I agree with @wildflowers
I live near Saint Paul, and those are the two that came to mind when I saw this thread started. Borage and Monarda grow wonderfully here.
Borage re-seeds easily, so you'll only have to plant it once. The seedlings look a bit like squash, so wait a bit before you pull them out next year. The flowers are edible and tastes me cucumbers. @dave
has mentioned that borage is a dynamic accumulator; meaning it takes up a lot of nutrients. So save some for the compost pile!
Let me know your thoughts and how your garden has done. It is good to hear about other gardens in the same climate. Thanks!