Redrockstraps sells a waxed version of their canvas strap. The price is about a $35usd premium over most of their other canvas straps. It got me thinking as to why you couldn't just do this yourself. I have re-waxed my Barbour jackets and a few other things, so it didn't seem to be all that complicated.
I have a thick canvas NATO strap which seemed like a good idea when I bought it, but less of a good idea in practice. I'm not sure if I'll ever actually use it, but it seemed like a good strap to use for testing.
I have a can of the Barbour wax on hand, but I decided against using it. In order to use it you basically melt the wax first and apply with a sponge or brush. For a watch strap I'm not sure you'd want something that is designed to penetrate that deeply. I also had some Otter Wax on hand that I've used for touch up, so I thought that might be a better option. The wax is basically the consistency of a bar of soap. Application is pretty simple. Rub the wax on with the bar, spread it around with your fingers. The heat from your fingers warms the wax and allows you to spread it evenly, so you have to keep working it around certain areas such as around metal parts, ridges, etc. Some people use a heat gun and the manufacturer says you can use one to soften the wax for more even application. I wouldn't recommend it for this since the strap is such a small area your fingers work better than anything.
The strap darkened a shade or two as I expected. There's a few hardly noticeable areas where the wax didn't absorb evenly so they are ever so slightly lighter. I'm sure a 2nd and/or subsequent coat would fix this, but it's not a bad look for canvas anyway and you really can't tell unless you're looking for it. I don't think I'd worry about doing another coat. Functionally the results are pretty promising. Water beads on the surface much more readily and doesn't soak in nearly as fast. I would expect a treated strap to be much more impervious to dirt and grime. There's just a bit of wax smell to it. It's not at all unpleasant and you have to get your nose close to detect it. This might change under normal wear as your body heat might make the smell more noticeable, but I don't anticipate anything detrimental. As far as appearance goes it definitely gives it a different look. I wouldn't really say patina because the look is more uniform, but it definitely looks more broke in and used with just a tiny bit of a satin finish.
At any rate if anyone has done this I'd be curious to know what the long term effects are. I might do some more experimentation with more some other unused NATOs I have.