If you check the forest service website, you will find things you might not expect:
Such as in the Inyo National Forest:
"In all wilderness areas shown, food must be stored in bear resistant containers, or counter balanced at least 15' above the ground, and 10' from tree trunk."
So no, a bear cannister is not required everywhere.
However, the only acceptable alternative in some areas is counterbalanced 15' above ground.
Which is hard to do without trees, and hard to do with trees, unless you have two foodbags that weigh close to the same.
That is why most just get a larger bear can, or rent a bearikade.
Its simpler, and less confusing, no worries about where to camp, etc either.
If you are SURE of the acceptable alternative approved by the forest service in each area, there is no problem. Most dont really want to research all of it and keep track. Just because theres no bear can required, doesnt mean there are no other food storage requirements everywhere.
However, all a ranger ever asks is "Do you have a bear can". They never ask to show that all your stuff is in it.
Most plan on 100 in3 per day of food (about 1.75" in bearcan), so 7 days = 700 in3.
The fewest Ive really heard of is someone saying they got theirs to 85in3 per day (about 1.4" in bearcan), which would be 595 in3.
Edit.- BV200 is 685? so would probably work.