I have always found DL to be extremely lenient with carryon pets. I would check them out as a possibility for this trip. They have never listed a weight restriction. @:-)

Pets As Carry On

Some pets can travel with you in the cabin for a one-way fee of 125 USD/CAD* (to be collected at check-in) for travel within U.S./Canada, U.S. Virgin Islands, and Puerto Rico (200 USD/CAD/EUR* for travel outside the U.S.).

Pets permitted in the cabin include dogs, cats, and household birds. The following restrictions apply:

Your pet must be small enough to fit comfortably in a kennel under the seat directly in front of you. Maximum carry-on kennel dimensions are determined by your flight. You must contact Delta Reservations to determine the appropriate kennel size.
Your pet must remain inside the kennel (with door secured) while in a Delta boarding area (during boarding and deplaning), a Delta airport lounge, and while onboard the aircraft.
Your pet must be at least 8 weeks old.
You may not carry on more than one pet.
Your pet in-cabin counts as one piece of carry-on baggage.
If you're traveling to Hawaii, your pet won't be able to go with you in the cabin, and other restrictions may apply. See Pets to Hawaii for more information.
*CAD amount will be charged exit Canada, and EUR amount will be charged exit Europe. Fees established by the contract of carriage in effect at the time of ticket issuance will apply.

Exception: Two pets of the same type may be allowed in one kennel, for example two dogs or two cats. They must be small enough to fit in one kennel provided they are compatible and must be of the same species and size, and they must meet the requirements of acceptance. They will be charged as one pet.

Also, Delta limits the number of pets per flight, but only one per passenger, to:
Class Number of Pets Allowed
First Class 2
BusinessElite® 2
Main Cabin 4


Pets are accepted on a first-come, first-serve basis. Call Delta in advance at 800-221-1212 to arrange to bring your pet on board.