You shouldnt need to worry about lens speed since it outdoors and likely sunny. You also will prob want to be further back than the "splash" seats, so you may not be super close. For that reason I would say go with the 70-200 and extender to be able to zoom in close (from your seats, 70 may still be wide enough for "wide" angles of the stage/tank). The only downside is if you want to take pictures with your group that will be harder - esp since to back up enough you will need space - getting people to stop walking between you and your subject in a busy park would be tough. If you didn't mind, you could do those people shots with the P&S and the DSLR of the whale show with the 70-200.
If it were me with your bag though, I would bring both the 24-105 and 70-200. YMMV
Canon 5DmkII, Canon 35mm 1.4L, Canon 70-200 2.8L IS mk II, Canon 580exII, Alum Macbook + Aperture 3 + Adobe CS3