Heavyweight canvas upholstry?  

I wouldn't, simply because cotton soaks up stains and dirt and is hard to clean.  Not sure how Scotchguarding it would work, if that wears off after awhile?  If you had to respray it, do you have to clean the fabric first?  I am also not sure about durablity.  A 15 oz canvas or heavier might hold up for 10 years.  I wouldn't go any lighter in weight than that. 
Linen---not sure about this either.  It creases almost like paper and might look sloppy as it stretches over the years.  I think the cleanability issues are probably about the same as cotton, given that they're both cellulose fibers.
I'd find a good quality synthetic blend with the look of cotton or linen, I think.  There are even some wools, like Maharam's "Steelcut", that have sort of a linen look.  

Oiled duck canvas, as in drizabone coats? That might work, smells good too but would probably wear quickly. Truck canopy ripstop seems pretty heavy duty.

Good imput, much appreciated. I'm thinking about dyeing and scotchguarding the canvas myself. I'll post results!