There are SEVERAL restaurants within walking distance of the Opera House. Here are just SOME. There will be a Tiger's Game the same day as the wedding at 4pm which will cause traffic and restaurants to be more full.
Detroit Beer Co.
1529 Broadway Street, Detroit, MI 48226, (313) 962-1529
Feel free to enjoy food at this restaurant before the wedding ceremony. It's right across the street from the Opera House.
Buddy's Pizza
Madison Building, 1565 Broadway St., Detroit, MI 48226