I would guess that there isn't a byob policy at the California Grill. Actually, I'm not sure there's a byob policy anywhere in WDW, maybe with the possible exception of wine you actually purchased IN WDW
(The next paragraph will sound snotty of me, so be aware, I'm not saying this is how *I* feel, but how I believe the management of California Grill feels)
Cali Grill is really upscale, fine fine FINE dining, the sort of restaurant that dining magazines will tell you to visit, even if you have no intention of going into any theme park. The sort of restaurant where management will be shocked and appalled to discover YOU think you can bring in a bottle of wine that competes in any way shape or form with their impeccable wine list (even if your taste in wine is better than their wine list). Granted, their wine list-their bar in general-will be pricey, but if you decide to dine there, it's kind of understood that you should expect an astronomical bill when you first arrive.
In short, if you've never been to Cali Girll, you'll know, when you walk in, that it's most assuredly not a byob kinda restaurant. If you really want to try, I'd suggest making up a cover story, like the wine you have is the same label and vintage from your first date, or something like that.