There is an excellent and detailed chapter about travelling to Cuba in Randall Kaufmann's book Bonefishing!...although he does not give up the scoop on how exactly to get to Cuba.
I also know that about a year or so ago there was a lengthy article in FlyFisherman about travelling to and fishing in Cuba. I do believe it is archived on flyshop.com...might check it out.
Ryan S. Petzold
aka Sparkey and/or Special