I picked this up today.  The leather strap with iron buckles is sewn to the webbing harness.  It's in rough shape, but all there and the stopper strap is leather as well.  The research I did said the leather straps are early production.  Would they still be using them with a Showa 17 canteen?

I've never seen a Mod 30 canteen with a issued leather shoulder strap, so I would think this is possibly a wartime repair.