Art stores do not always carry the canvas size you want. More importantly, art stores sell canvases that are as loose as flags. So I started making my own nice, tight and springy canvases! Eventually, I made a tutorial on making your own canvas.
And one thing I learned is that clean corners and sides make a big difference in the presentation of your art if shown unframed. Thick profile canvases are often hung unframed but messy sides are not too appealing.
It took me a while, but I figured out a way to fold nice smooth corners. If done well (and I am still practicing) it would not look like the panel has fabric stretched over the bends of the wood bars.
Click on "Stretch a Canvas" in the top menu, or click here and scroll down for the details.