Assiniboine hunting bag and horn from the early 19th century in the Smithsonian collection.
Similar style of bag on this image of a early 19th century Canadien.
     As far as I know, there are no Canadien leather hunting bags from the mid-18th century still in existance.  Period images show very few bags, and many of those bags are more along the lines of native styled slitpouches on the sash or horn such as the images of the couers de bois and the milicien on snowshoes.
     I made this bag to fulfill the need to carry a water filter while in the woods and to use to hold gunpowder cartridges while at battle reenactments.  I based it off of the Great Lakes example from the Smithsonian and from the painting on the left.
      I figure that basing it off of something in the historical record is better then pure speculation.
      The horn is a simple corn horn with no engraving and designed for functionality rather then artistic merit.  Horns from this period of Canadien orgin are as well very rare, and so keeping it simple is the best approach in my opinion.
Hunting Bag and Horn
                 Water Filter

 
The times when an explorer could dip their hands into a lake and drink the fresh and safe water are long gone.  It is a necessary tool in these modern times to carry some sort of water filter that will deal with the biological organisms (like giardia) that could make you ill in the short time you are in the woods. 
     I have used many different filters over the years and am very happy with my Katadyn Hiker.  It is lightweight, easy to use and clean, and has gotten rave reviews by many other backcountry folks over the years.