Thompson's Water Seal for sealing (deck) wood works well. If you can hang the canvas somewhere and paint
it on both sides, let dry, repeat it lasts longer. Our last treatment lasted three years. Find it at any Home Dept/Lowes/hardware store. A gallon goes a long way....you'll probably have left-overs to save or give away.
The 3M can stuff didn't last as long, for us.
I wouldn't catch drinking water
off the Thompson's treated canvas...you can see an oily sheen on puddled water.
best - J