If you post the flight numbers, I can tell you exactly what it will be.
However it will most likely be the plane pictured above.
The one pictured above is a Canadair CRJ which seats about 50 people. There is a larger version that sits about 70 however I don't think Delta Connection has many of those in their fleet.
The CRJ is a great plane to fly. It is two by two seating and there is one attendent on board. The seats are a bit smaller than regular airline seats though. Also the windows are lower than usual and if you like to look out the window (like me), then your neck may tend to hurt.
Delta Connection also flies Embrear ERJ 145 jets. Again they are similar to the above but made by a different manufacturer. The seating is also a little different where it is one and two seating. The windows are also bigger and provide a better view.
My preference would be the ERJ over the CRJ.
The other regional jet that Delta Connection flies is a Dornier 328 Jet. The difference here is that it is a high winged airplane and the engines hang from the wings. Cabin layout is two and two and the views are all excellent since the wings are above. Delta Connection does not have many in their fleet and I've heard rumors they wish to phase them out.
In any event, all three are state of the art airplanes. Enjoy your flight.