It's hard to imagine the two elements, Vecna and Giants, tied together. Sure they can, but it's hard to imagine what, so I won't.
I suspect the Vecna product may be a long way off, and will not be this year. The timing between statues/miniatures and books are often way off, like the sapphire dragon dice and eventually Fizban's (that was at least a year, maybe two?)
The giant stuff is either this fall, or early next year. I think it will be the First World, a new setting for "pre-historic" D&D games in the world ruled by dragons and giants. A giant-centric book in the vein of Fizban's is possible, but I personally think unlikely... giants got a fair amount of coverage in Volo's, and making an entire book about theme (although possible) seems like a topic the D&D team wouldn't retread.