AMD cards don't support CUDA.
That's correct, AMD has announced that they support OpenCL as the GPGPU language. And OpenCL is an open standard as opposed to CUDA (NVidia proprietary).
which one could be running wesnoth in the future?
Forget the "future". Maemo already runs Wesnoth, and quite well at that.
We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise. -- Larry Wall