To make my waxed canvas, I melt organic beeswax and work it into pieces of my hand dyed fabric. I have experimented with many variations on waxes and oils but have found that I prefer the the look and feel of pure beeswax.
Why waxed? While waxing does provide water resistence, it's more about the look, feel and wear of canvas that has been treated with waxed. Like leather, it can get a nice patina and grow richer with age. I absolutely love the look and feel of waxed canvas!