I have done it both ways, on ceilings too, (the last one was 17x22) and the effect is better if you don't cut it, plus you won't have the extra work of touching up the seams, which can be tricky. Cut your canvas with 2 to 5 extra inches all around, to allow for shrinkage (most of it will occur as you prime) and so that when you install it there is a comfort zone in case of problems.
The best way is to be well set up, with enough scaffoldings to cover comfortably the surface where you will have to move, and set them at a height where you can comfortably stand while touching the ceiling with your arms not much above your head. You need to have your canvas rolled up, ending with the side that must go first. Have the ceiling prepared with two coats of special glue (let the first coat dry a a bit before you put the second coat), and slowly and with the help of two others, unroll the canvas unto the surface, positioning it as one of you pushes the airbubbles out of the canvas with a wide brush, just as when applying wallpaper. But if you have never done it or seen it done, and it makes you nervous, give the job to an experienced wallpaper professional, if you can find one who is up to it.
Good luck!