Here's a few thins that mention canvas and cloth.
George
The Col. Is desired to collect in Virginia as many Powder horns as can be got, all that can be had from Pensilvania shall be ordered... For Shot Pouches, osnabrug [a course, unbleached and cheap linen] will be bought, with thread to make them one yard will make 8 bags.” (Bouquet to Washington June 13, 1758 George Washington papers p 208).
Appendages of the Gun A Treatise on English Shooting; by GEORGE EDIE, Gent. London 1772
"A leather pouch, or small canvas bag, to carry the shot; with a tin, or other meaasure..." p9
October 12, 1775 2d Va orderly book:
“… Each Company is to draw a sufficient Quantity of Dutch or Russia Drilling to provide Each Soldier with a Shott Pouch with a partition in division in the middle to keep buckshot and bullets separate. Each Soldier to make his own sack and Shot Pouch as near one General Size Pattern as possible