Any more information? I'd run it through the wash if it's small enough. I'm assuming no paint or other decoration? Beating it and air blowing won't get all the dust, I've tried that with a tent. Hosing the tent didn't work well, either, so I put the tent in the tub with a quarter cup of Lysol, then do the same with the fly -- they aren't canvas, and aren't washable.
Cotton canvas will shrink in length to some extent, so asking what you should do to clean it isn't offering enough information for good replies.
Playa powder will have some abrasive effects on the canvas -- but without knowing what you do with it, I can't guess how much. Playa powder is harsh stuff, and I recommend removing it if at all possible.