It appears there is confusing information about bear canisters in the North Fork/MR. In 2003 when I was there (backpacking) they were not required. My permit confirmation for June 2004 says bear canisters are
Required in the Onion Valley/Kearsarge Pass area...Bishop Pass area....Mammoth Lakes/ Rush Creek area...Little Lakes Valley and the Main Whitney trail.
They are "recommended" in all other areas.
Fishbaits comments explain why there has been confusion, since the two trails share the same starting point. I go under the assumption I don't need to take a bear canister up the North Fork, and never have. That seems reasonable, taking into consideration the rules the forest service personel in town have reviewed with me when I picked up my permit.