When hiking, I put my camera and long lens, (in case of suprise wildlife), over my shoulder, bandolier style. A small bag with a wide lens sits in reach on the side of my pack. As the the trail gets rough and I have to scramble, I clip the camera strap to my pack's waistbelt using a climbing-gear racking device called an ice-clipper, (the strap goes around my neck, shoulder and the ice-clipper). This effectively immobilizes the camera, but you have to unclip it to use it. My pack has slots for the ice clipper, but you could rig something together with cordage and a carabiner.
Third party neckstraps are much more comfortable than the Canon ones. Mine is a neoprene material that is confortable even after 20 mile days.
Your setup is much heavier than my backcounty kit, so you may have to experiment with what fits you equipment/style. Take a few long day-hikes experimenting with different systems. The main thing is to reduce swinging and chafing.