If you just need camera luggage that you can strap on your back once in awhile, I suppose the generic camera backpacks are ok. If you need to haul your gear far away from transportation, then a proper backpack is in order. I own several real backpacks and panniers for my bicycles. I am partial to Dana Designs, Odprey & Jandd Mountaineering simply because that's what I own. After some trial and error, I arrived that the 3 brands mentioned and haven't felt a need to look further. There are many other good brands of backpacks.
Both backpacks have internal frames and great suspensions. The Osprey is a panel loading all day to maybe weekend pack. The Dana Designs Terraplane is a classic top loading + bottom compartment load hauling monster. I'm sure I could put more stuff in it than I could pick up. The bicycle is outfitted with Jandd mountain bike panniers & handlebar bag. All 3 brands are built to last. Actually, built better than they have to be. I apprciate that when I have to load them up.
I thought this was about cameras?
I have pondered loading my camera gear in my various packs. I thought I would have to make this a D.I.Y. project. Then I discovered Photobackpacker.
Link to Photobackpacker
These folks make a series of camera and lens cases that will fit in standard backpacks. They also offer a decent Kelty pack to hold their cases. You'll need to do some measuring to make sure your gear will fit a particular case. From the dimensions, I think they have a case large enough for the Canon 70-200 L.
Lens cases:
Camera & lens cases in a Kelty Redwing:
I think that with some careful measuring you could fit these cases in an empty Pelican box too. If you run across a used Pelican box with shredded foam, ditch the foam and add Photobackpacker cases.
Final point: Until you have toted a load with a real backpack, you can't imagine the difference that a proper backpack suspension system makes. The camera bag backpacks don't come close.
Enjoy!