It's designed for the Sony PRS500/505, so it's a mite bit *too* shallow for the cover to hold down without some form of strap or latch. You'll see this when you look at the image of the side of the case with the lid on. But the Cybook *will* fit in the case length and width-wise, even if the Cybook is in the old-style leather softcover case. As I don't have the *new* style softcover case, I can't say if that case is thinner. If it is, then you'll have no problems whatsover using this eCaddy with your Cybook Gen3.
I note again that doing an eBay search for "titanium eCaddy" will show plenty of auction listings.
Derek