I am a huge fan of the flexylot canvas/picture frame holder (https://amzn.to/3XIvkGA) but in this particular case I had to go much higher than I expected when I was drilling the hole. To avoid drilling another hole I just created this higher holder you can screw in the wood of your canvas.

I printed this accidentally without any support and upside down but it worked out ok since the ugly side is the one that is not used to support the canvas. If you have a bigger printer you can print it laying also without any support.