There are three main ways to orient a bear canister inside a pack, but the best way depends on the dimensions of your particular canister and your particular pack. A round cylinder is the strongest practical shape.
1. You can orient it with the axis straight up and down. This fits a small pack best, but it puts maximum pressure against your spine.
2. You can orient it with the axis right and left horizontally. This fits very poorly in a small pack, although it works OK in a very large pack, and it tends to put the canister weight more on your hips.
3. You can orient it with the axis forward and backward horizontally. This puts the top or bottom flat against the spine, and this works the best for me. However, I use my BearVault 450, which is not a very tall canister.