FWIW, my BV450 (8.7" X 8.6") will probably fit in most panniers and if not it's little brother the BV425 (8.7" X 6") most likely will. Given that we can restock food often when road touring I find that we don't need to carry a lot of food. So if I were to use a canister on tour the 450 or even the 425 would suffice for a road tour.
That said the notion that touring without a canister is illegal anywhere. I have toured through quite a few of the national parks that require a canister for backcountry camping and did not use a canister for touring. It was quite legal since there were bear lockers in all the campgrounds and dispersed camping would have been illegal other than backcountry camping with a permit. When I backpack in these parks I use my canister, when I tour I use the provided lockers.
I did run into minor issues in a couple places where a state or other park said to put food and scented items "in the trunk of your vehicle". There always was some solution like in a state park outside Yosemite where we were able to make friends with a neighbor from a nearby campsite who let us put our stuff in their car trunk.
Where there aren't specific rules against it I hang food in areas with bear risks. I have a lot of experience camping in bear country touring, backpacking, and canoeing and have't had bears get into my stuff yet. Raccoons yes, bears no.