The box does indeed look to be an Enfield Cartridge Box, and the canteen looks correct for the U. S. Civil war as well, though it is riding a bit high.
The haversack isn't showing me enough detail to identify it, and I'm not really sure about the musket... lack of a ramrod, barrel bands, and sling cry out 'Photographer's Prop!'
He also looks a bit old for a CW era soldier, (though my G-g-grandfather was 38 when he enlisted in '61) and his hat looks more like a fraternal organization hat.
I'd almost bet it's a post-war pic, perhaps of a member of a veterans' organization.