Since that’s not a standard resolution there probably won’t be many (any?) premade backdrops that fit perfectly. Some 1280x720 images might work well enough if you don’t mind the top or bottom being slightly cropped.
Depending on your display hardware, though, you might be able to run an actual 1280x720 Workbench with one of the newer monitor drivers.
Otherwise, be prepared to rescale some images manually.
