Bear populations, bear problems, and aggressive bears are distributed extremely unevenly in California wilderness areas. There are dense populations of problem animals in a few small areas such as Yosemite Valley and Little Yosemite. These are areas with a lot of humans packed into a small space. You're going to the White Mountains, which gets very few human visitors, so you're not going to be in one of those areas with a high probability of bear hassles.
Yes, bears that are used to humans will definitely steal your food right away from you. I've had a bear steal my crackers when I sat down to eat them. A friend had a bear rip open his pack while it was on the ground nearby.
"Do I really need to keep my food in one of those while hiking?" This question doesn't make sense to me. You have the canister in your pack, taking up space. Why would you not put the food in it?
Bears operate more by smell than we do, so they're most likely to detect your food by its smell. You can cut down on the smell by putting all your food in ziplock bags, inside your bear canister. There are special brands of large ziplock bags such as Aloksack that are claimed to be more odorproof than normal bags. They're convenient, because they're big enough so that you can get all your food inside a single bag.
At night, simply put your bear canister at some distance, say 30 m from where you're sleeping. If a bear does find it, it may try to break into it, but it won't be able to, and you won't be up all night because of the noise.