Manufacturing Question: CNC or Casting?

I've got a question for my manufacturing friends out there. Lets say I'm building something that requires some aluminum (or similar) parts to be created about the same size as a small block chevy motor, but hollow with about an inch or so thick walls. The "box" could come in multiple parts per wall and fastened/welded together or whatever it takes to save on wasted material. If we're creating ~1000 of these boxes per year, should we use CNC/subtractive or some sort of casting? What are the pros and cons of each?