I asked the local trimmer the same question when I needed a canopy cover as well, and he steered me towards canvas. If I remember correctly he said the PVC tended to trap moisture in the canopy because it doesn't breath, and was hotter than canvas because of the same reason.
I have had the canopy on for 10 years now and have had to replace the rear zips once. The canvas is nothing like the colour it was originally as it has taken on a red dust hue, but the canvas is good itself.
Having had utes with tonneau covers, I would prefer canvas for a canopy, but the PVC would wash up better.