You might be overthinking the requirements - it's actually very straightforward. Since I'm in the same boat as you - I live in SoCal and hit the high Sierra primarily to fish - I've gone through the same design processes.
Over time, I've made a series of packs. Some are designed for bear cans if I'm going into/through a NP *and* I think I might run into a ranger (think: either hiking portions of the PCT or crossing nearby). Other packs have been constructed for non-can uses - either I'm purely XC in a NP, or I'm in a non-can required section of the nat'l forest.
OK, so here's the easy way of constructing either pack: simply roll your pad into a cylinder and place (stack) all your items inside. Most likely, you'll find the can determines the maximum circumference. (If your bag/quilt is setting the max, I would highly recommend making your own stuff sack so the bag ends up just under the can's diameter.) Once you have your kit assembled, simply measure the circumference & height and get cracking.
Now, here are a few secrets that I've discovered through trial & error:
* Make a simple stuff sack pack with a tie top, sans pockets, etc. I've come to realize they're a hassle to add, add -0- or little functional value, and can actually weaken the overall bag. Now, with the exception of my rod(s), everything I have simply goes inside. (If it rains, I have all my stuff inside in turkey bags anyway.)
* Even though traditional packing emphasizes putting food/can in the middle, it doesn't work without a rigid frame pack. That's because when you put the pack on, that can is sitting right there between your shoulder blades & middle back. That's right - you look & feel like a chicken with your wings splayed out.
The solution is to put the can either on the very bottom or the very top; of course, with food inside, it makes the weight balance unmanageable. So the trick is to *pack/handle your food as if you didn't have a can in the first place* and store it in the middle of the pack as you normally would. This in essence renders the can a 2lb deadweight (well, I put misc items inside to fill it up) that is there merely for legal purposes (I do use it at night since it's there), but it can also be turned to your advantage as part of the pack frame - here's how:
* Put the can on the very bottom - when you put your pack on, you'll find it's now way down in the small of your back. If you fit the pack properly, you might not even notice or feel anything down there.
* Measure your dimensions carefully - if your total circumference is just right, the can will fit very tight & snug. This adds a lot to rigidity; in fact, I barely need compression straps. (As an added benefit, it also IDs the exact location where you want to place the bottom edge of your hip belt.)
* Even though you measured/cut/sewed the pack as a cylinder, fold the pad and place it inside square against your back. This will create a triangle effect overall (ie the can resting against the pad), but it makes for a nice flat surface against your back.
If you want to add stays, etc, just include the add'l allowances in your final cut measurements. You mentioned cuben, but I'd practice first with a yard of cheap 1.9 from JoAnns. In fact, my bear can pack is made from 1.9 and only weighs between 7-8oz, whereas my non-can pack is made from 1.3 sil and weighs around 6oz.
My 3 night total packweight with can is 13lbs, dropping to 8.5 on the way out, whereas my 3 night pack sans can is 11, dropping to 6.5 on the way out. Yep, around 4.5lbs of food for approx 3.5 days, where I typically cover between 35-45 miles.