If you are backpacking in the Sierra you will likely have to also carry a bear canister. A 40L pack is quite small and most likely will not accommodate a bear can. Depends on how many days- there are small bear cans designed for 2-3 day trips. But if going a week or more, it would be tight.

If you try the pack on at a store, see if they have a bear can so you can see if it fits.

The only way you will really know is to buy the pack and then fill it at home and carry it around the house a for a few days to see how it feels. If it is not right, send/take it back. Definitely do not buy a non-returnable item and be sure to leave on all the tags until you decide to keep it.