Place the roll of canvas on a flat surface, such as a table, and unroll the canvas. Position the stretcher-bar frame on top of the canvas. Cut the canvas, so there is at least one-inch overlap all the way around the stretcher bar.
Fold one side of the canvas over one of the long sides of the stretcher bar. Place a staple through the canvas and into the wood stretcher bar near the center of the bar.
Turn the canvas and stretcher bar, so the side opposite the first staple is facing you. Pull the canvas toward you, until the canvas is taut, and wrap the canvas over the bar. Place a staple through the canvas and into the wood near the middle of the bracer bar.
Turn the canvas, so one of the short ends is facing you. Pull the canvas taut, and place a staple through the canvas near the middle. Rotate the canvas, so the last side is facing you. Pull the canvas taut, and place one staple near the center of the bar to secure the last side.
Finish stretching the sides of the canvas by pulling the canvas. Place a staple about one inch to the left of the first staple. Pull the canvas, and staple it to the right side of the first staple. Repeat this process all the way around the canvas. Finish the sides by repeating the process, until there are staples approximately one-inch apart along all sides.
Create sharp corners on the canvas by pulling the two sides of the canvas together at the bottom-inside edge of the corner. Fold the top flap down. Pull tightly, and place a staple in the center of the fold to secure the canvas edge.