It depends on what you consider walking distance. To get ack to the "mainland" from the port where the ships actually dock would be a good mile walk. There are resturants in the Bayside area, but again it would be a hike. June 22nd is going to be very warm too. You might be walking in very hot humid conditions.
If you can drop your luggage off at the port, then you could possibly walk to bayside, but its not a terribly short distance. You might be better off having the taxi drop you and your luggage off at your sister's hotel, then finding breakfast near the hotel and all going to the port at once (even if seperate taxis are required).
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007