Cathay Pacific, like most non-US carriers, are VERY strict with carry on bag limits. If it is over 15 lbs (and a lot of the time they do weigh them at the gate) you will have to check it.
You will have a better chance if you can carry on your bag on the LAX-HKG route.
Since you have to go to the ticket counter anyways to check in remember you might be checking your backpack. If you are flying out of HKG on Thursday’s there are two flights one with CX the other with dragonair.
I used a ZED on CX once before and had a seat assigned 4 hours before the flight.
MyIDtravel actually shows the AA LAX-HKG/CX HKG-DPS as an option so MyIDT thinks the connection is possible, however accurate that is.
Good Luck