I've used artist's canvas for my terrain mats painted with house painting acrylics (eight colors on my main land mat). Not really sure what a canvas sheet is that small. I'd recommend forgoing the sheets and move up to a drop cloth. You can paint them in different ways for different battles and while I've not tried it, you can probably paint over the first coats to get entirely new mats - at least until the paint gets too thick to keep going.
That size, if loose sheets of canvas, will be a major league pain, I'm thinking. Probably meant for stretching over small frames for 'real' painting.