Hi Lisa and fellow Nebraskan,
We just returned from WDW and had ordered a custom cake for my son's birthday, and it was perfect for him. He had just recovered from chicken pox, so the bakery had placed Chicken Little with chicken pox on the front as well as a clever message. The cake hotline is 407-827-2253.
I believe that each restaurant has its own arrangement for where the cakes are made, so I honestly don't know about having it delivered from the Grand Floridian. If there is something special that is done from that bakery, I would imagine the California Grill would try to do that as well.
Sadly, there isn't an official website to view the different cakes. However, you can do a Google search for WDW birthday cakes and then select the 2nd choice from wdwinfo.com. It will lead you to a page where you can select the "Official Birthday Cake Thread with photos." It has a huge collection of photos of cakes that guests have ordered.