The tent pads are raised up on railroad ties. The better sites are the ones that the pads are level to the ground. You could fax in a request for Loop 2000, sites 18-22 backing up to the canal. You may or may not get it.
That being said, for a secondary request, I would ask for near Creekside Meadow and the Comfort Station. There is a bridge over the canal in Creekside Meadow that leads to the 900 loop and then on the the Meadows Trading Post.