All depends on how you are going to display it. With a 26" wide print you'll have have 5" borders on the long axis on 36" wide paper, of course, so what size do you want it matted/framed?
For a print this size, leaving at least couple of inches under the mat is a good idea, and I like to leave a reveal of 1/2-1" around the image. So it seems to me that a 24x36" paper size with a centered image should be adequate, leaving 3" borders on the short axis.
Pete
