Yes, canvas can be waterproofed. There are several ways to do this, but the most common is to treat the canvas with a waterproofing agent. This can be done either before or after the canvas is sewn into whatever final product it will be used for. Waterproofing agents work by creating a barrier between the fabric and water, which prevents the fabric from absorbing moisture. This treatment will not make the canvas completely waterproof, but it will significantly increase its water resistance.