The Canon 7D’s sensor is 5,184 × 3,456 (~18 MP). That’ll get you approximately 20 inches of print suitable for a viewing distance of 2 feet, (according to the chart above). If you want say, an 8 foot wide banner, you’ll need about 4 photos stitched to get the print quality that you want. I’m going to say that you’ll be fine with 150 DPI, which will give you about 30 inches of print per photo.
Again, I think your best bet is talk to the person in charge of printing, and ask them what their printer is capable of, and what DPI you need to aim for.