Good idea for a discussion!

I agree with you on emphasizing the difference between the Ettinsmoor giants and the Harfang giants... Lewis describes the giants at the gorge as being almost grotesque, whereas Jill thinks that the king of the Harfang giants is good-looking as far as giants go, with a good nose and a fine beard. Even they, though, are not exactly human-looking, so I would imagine that at least some prosthetics might be in order to create the desired effect. The Ettinsmoor giants, on the other hand, might require CGI (especially since they're initially camouflaged in the scenery), but I don't think that would be the end of the world given that they don't figure into the story very much and should have little screen-time.

And then there's also Father Time, the greatest of all giants, who lies sleeping in Underland: his face is described as not like the giants but "noble and beautiful." (I've always imagined George MacDonald when I read this part.) I hope this part of the book isn't cut! Since Father Time essentially just looks like an enormous man, it wouldn't be very expensive to include, and it's rather important for The Last Battle.

I like the idea of using CGI sparingly with the giants. For one thing, CGI tends to age pretty quickly, even though it's come in leaps and bounds. For another, I think size doubles and set scaling and perspective can have very nice results (I'm mainly thinking of the LotR films, particularly Gandalf and Bilbo in Bag End ). Of course Hobbits and Giants have rather different scaling, but I think the concept would still work fairly well.

Also, good point, Rose, about Father Time. I do wonder how they will do that part, and I hope it isn't cut. I don't have my book handy to check the description, but do you think they might put him more on "display"? I could see the party entering more of a cavern in which Father Time is sleeping on an elevated table/slab in the middle of the room.

I guess I kind of assumed they would use the same technique that they did with Gandalf and the Hobbits and Dwarves in the "Lord of the Rings" movies. Two different shots with stand-ins so the actors know where to look and interact with the others that aren't really there. I assume building two different sets and props and whatnot is cheaper than CGI.
I would think at this point CGI has become quite a lot cheaper than it used to be.