Measure the width and length of a vintage sugar sack.  

Head to your local art supplies store and find a white canvas in the approximate size of your sugar sack.  Keep in mind you will need to account for the 2 inch sides of the art canvas, so depending on the scale of print featured on the sugar sack, you will want to pick a canvas size that allows you to best feature the entire printed area of the sugar sack.

Position the sugar sack into place on top of the canvas.

Carefully staple the fabric to the back side of the canvas, starting with four staples; one staple to the center of each canvas side.  These four staples act as anchor points from which to staple the rest of the fabric taught.

Pull the remaining fabric taught and staple into place. Be sure the staples are not visible.  

Hang your sugar sack and enjoy!