Great video, looks like a well adjusted happy pup!
Sonny took right to it and had no problem. He wears a harness on walks so he was already used to the process of something going over his neck. I took him backpacking one and we did twelve miles in one day with up and down and some bushwhacking and he never once gave any sign he was not liking it. He had 64 oz of water and about 4 cups of dog food , some treats, a collapsable water bowl, a bandana and a toy.
My previous dog never wore one but I never tried with her. She did wear a harness and never had any aversion to it though.
Sonny has a Ruffwear pack
https://ruffwear.com/products/hiking-dog-pack-approach and a Ruffwear harness
https://ruffwear.com/products/front-range-everyday-dog-harness Ruffwear is pretty much the industry leader for quality functional stuff for the outdoor adventure dog. There is also good stuff from the sleddog companies but it's mainly collars, leashes, harnesses, also seasrch Canicross. Neewa out of Italy makes quality stuff
This is the leash Sonny has because he needed all metal hardware as he has broken three leashes from Ruffwear and Stuntpuppy ast the plastic quick adjustment they use (never had an issue with any of my other dogs using them but Sonny is a puller and lunger).
Anyway I'd suggest getting the daily walking harness I listed above. Ruffwear has a lot of copycat ones now but durability and ease of use and innovation is what makes Ruffwear worth it (they are kinda like Patagonia of the 90's before Patagonia went Gucci). If your dog takes to the harness he should have no issue at all with the backpack cuz it's the same exact process and feel except he'll be carryin a bit of weight.
*edit* now with pic (you can check my Flickr to see some of his regular harness as well)
Sonny by
yobbodobbo, on Flickr