Hello. My understanding is that, for trips in Sequoia NP or Kings Canyon NP, if you are able to use bear boxes, you technically do not have to carry a canister, though they are highly recommended. But I would confirm that directly with the national parks -- their webpages have maps that explain the food storage requirements in the different jurisdictions. Here are some links: http://www.nps.gov/seki/planyourvisit/bear_bc.htm, http://www.nps.gov/seki/planyourvisit/upload/2012-SEKI-Allowed-Food-Storage-Containers-7-12-12.pdf.

This discusses the location of the boxes. http://www.nps.gov/seki/planyourvisit/bear_box.htm

At Tyndall Creek, once you go toward the ranger station, there is only one bear box, and it is located in a yucky campsite after the ranger station, a long way from the JMT. If you do not take the Tydanll Creek trail at all, you'll do better for bear boxes -- there are more boxes right off the JMT near the intersection with the Tyndall Creek trail and Frog Pond. (If you do have your own canister, then camping along the Creek on the trail that goes to the ranger station is pleasant -- easy water, lots of sandy spots, not many people.)

I don't recall where the boxes are that are near the JMT/Kearsarge intersections. There certainly were a ton of boxes, and well-established campsites with firecircles, after the intersection, when you drop down to 9300' or so and start hiking south along Bubbs Creek. (BUT SEE LINK ABOVE: AS TO THIS AREA, NPS SAYS "CANISTERS REQUIRED, FOOD-STORAGE LOCKERS FOR PCT & JMT THRU-HIKERS").