"You might get hassled by a ranger, but he's more likely to not even notice, so long as you show him your bear can."
Rangers out on trail patrol tend to have a pretty good feel for bear canisters and how much food they hold (and how many days of travel that equates to). Normally, they can just glance at your pack size with its bulges, and they can tell if you have a bear canister or not. Once in a while, they will reach over and bang it with their knuckles to know that it sounds like a bear canister. If it all seems kind of wrong, or if your answers seem wrong, then they will ask to see the canister outright. That means unloading your pack out there on the trail until the ranger is satisfied. More likely, however, they prowl around in the late afternoon and early evening, just when people are setting up camp. Then, they want to see it. One ranger actually wanted to see the backpack dumped out so that he could tell that you didn't have a bunch of food extra that would not fit into the canister.