I do all my work in acrylics on wood panels instead of canvas. I prefer by far using a hard surface since I layer a lot of paint. But, mainly, I distress paintings with gusto, using sandpaper and all sorts of gouging tools from dry points to screwdrivers and knives. A canvas absolutely cannot withstand this treatment, neither does illustration board, although I made a couple of paintings on the latter and it was more forgiving than canvas, but was way too porous, and sanding didn't work very well.
What I like best is when I sand is that the results are usually beautiful. This process allows me to get a softer, worn out look, sometimes even grunge-like and adding a glaze or paint on top is like the cherry on the cake. I can build much depth, and no other surface allows me to do so.
I also, on occasion, add collage to my work and paper glued onto wood is perfect, since it's made from trees. There are no issues as long as you use medium properly and here too, the result is gorgeous. Same with transferring an image from a laser printer copy, which I'm starting to explore some. One more process is using artist tape to get very straight lines, and that would not work so well on canvas.
My favorite suppliers are RexArt and American Easel. RexArt even creates custom sizes.
Here are the links to their sites: