I would agree with jPaul on shipping that canvas. It isn't that expensive to have it restretched after you receive it. It can be shipped flat but you are leaving that flat open expanse of canvas open to most anything that may be dropped on the shipping carton between there and here. Once something punctures the box, you probably will be paying much more to have the canvas repaired. (And probably a restretching fee also because they will have to unmount the canvas to repair it.)
If you are up in the Panhandle, bring it by our gallery and I will restretch it for you! We deal strictly in original oils and have a stretching machine as we receive all of our canvasses unstretched and may have to stretch 50 or 60 at a time when a large shipment comes in.
Framerguy