Have you talked to a stone fabricator to see if what you want to do is reasonable? 1 1/4 (3cm) thick granite is probably close to 20 pounds per square foot. Serious injury will happen if the slab falls off that wall. If you want to hid the plywood substrate and you are doing a slab, your best bet is to use a thinner slab and have the edges doubled up. This will give the illusion of a thick slab while hiding the substrate.
I still think you should talk to a fabricator before going further.
I'm going to, thanks. We are also considering a tile countertop...heard that looks nice.
I did a butt joint on 12"x12" granite tiles on the counter top in my rental. It looks really sharp and minimized the grout lines. The store I got them from had a prefabbed edge moulding, made of the same granite, that covered up my plywood base.