After printing and letting my canvas dry a day or two, I coat them with liquid laminate.
This not only makes the canvas pop with brilliance and enriches the blacks and other colors, but protects the image from scratching and makes the print layer more flexible for stretching. Stretching uncoated canvas can be done, but the canvas is very vulnerable to damage without the coating.
Once coated, the canvas is very flexible and besides physical protection, the coating will also protect against UV, many liquids, finger prints, etc.
In my experience, the canned spray-on coatings are just not enough protection. You've got to roll it on, use a HVLP sprayer or tray laminator like the Daige EZ Glide.