This is an easy project that requires zero skill and no time, and uses items that you probably already have lying around the house.
Just so you know how fast this was to accomplish, I waxed my husband's canvas flats during the period of time it took for him to take a shower. So about 10 minutes.
He has been complaining about his shoes (and socks... and feet) being completely soaked when he wears these on rainy days.
I decided that fiiiiiiiine, I guess I'll wax them. I don't know why I resisted. I guess it just felt like another chore on my neverending list of chores. But it was that, or listen to him complain until July when monsoon season finally ends in Seattle, and NOPE. Couldn't do it. Waxing is definitely easier.
First things first, you need wax. I used snowboard wax, but you can also use a regular old candle, or beeswax. I don't think it really matters.
Then you just rub it on the fabric of the shoe. I rub it in pretty thick because I'm an overachiever like that.
Next, you use a blow dryer on its highest setting, to basically melt the wax into the fabric. You'll know it's done because the color will return to it's original shade. This is pretty fast, by the way. No need to spend tons of time on this phase.
If you touch the fabric, you can feel that it is slightly stiffer now and has a very slight wax residue. It shouldn't be super noticeable or thick though. It should still almost exactly look and feel like the original fabric.
If you're not sure that you've properly waxed the shoes, you can do a second coat of wax, following the exact same steps. (Remember, though: It's better to do multiple thin coats then a single thick, sloppy coat). One coat SHOULD be enough though. After one coat, the water just rolled right off this shoe. I only did a second coat because my husband is really hard on his shoes. He'll come back from picking the kids up from school, and his shoes look like they've been through 'Nam.
Note: I do recommend an annual rewaxing of any shoes you choose to weatherproof this way, or more often if you notice that water is being absorbed and leaking through. Wax does in fact wear off eventually.