c/y mount versus contax rangefinder mount?

Are c/y mount and contax rangefinder mount the same?

Will this be able to sit on a c/y adapter? If not can it be adapted to EOF with infinity?

http://www.ebay.com …enses&hash=item​3a806ff3a5

No.
Rangefinder has a shorter register distance - no infinity on EOS EF

All rangefinder cameras I'm aware of use a much shorter register distance (measured from the rear of the lens to the film/sensor plane) than SLRs. This is the distance the lens is designed to focus upon. I forget the exact numbers, but Canon EOS/EF register is around 45mm and I would guess most rangefinder lenses are about 25mm (in order to keep lenses and cameras compact). That's a huge difference, in terms of adapting a lens. So it's pretty universal that rangefinder lenses are not usable on a DSLR/SLR, even from the same manufacturer. They might be usable on some of the new mirrorless models, though.