So far it seems the only ones broadcasting in 4K are Rogers and Bell. It's not Bell TV, their satellite division, but Bell's cable division and they are both out East.
Shaw will likely be first out West but there's limitations right now with the Rogers 4K as I believe all you get is a 4K box with no DVR capability. As much as I would like to go 4K I'm at a stage where I can't give up my DVR. It's also likely going to come at a premium when they do have a DVR solution due to the larger HD space required to record 4k programming.