I have had success with mounting canvas on the wall by first attaching
1 inch by 1/4 inch wood strips around the perimeter, then stapling a large canvas to the strips.(I used a brad nailer as I was attaching to panelling - drywall may require plugs)
I used regular house drywall primer as a base and the canvas became drum tight. This kept the canvas off the wall slightly and painting on it was similar to a gallery wrapped canvas. I added narrow strip molding on top to hide the staples after I finished painting.
I used a canvas painters drop cloth (10x12) which was really cheap. It did have a seam which I placed at a height where I was incorporating a chair rail but I was pleasantly surprised to see that it virtually disappeared once I had primed the canvas.
We recently had to drywall the adjacent wall after installing new french doors and it was easy to just undo the staples, roll the canvas back out of the way and re-staple when we were finished.
I'm almost tired of this mural and am contemplating whether to re-paint over it or take it down, roll it up and store it away. Either way this method is very convenient. Good luck.