If you already own a .30/06 class rifle, you're good to go, but if you want a bison specific rifle, things can get very interesting depending on the thickness of your wallet. Nostalgia suggests a big bore black powder cartridge, a .50-110 should make the 2800 ft-lbs required. But if you prefer modern cartridges, you could try anything from a .338 to a 600 Nitro. But a modern rifle chambered for a medium velocity cartridge loaded with heavy for caliber bullets provides the best answer IMHO.
A pal of mine killed a couple of dozen in the course of a cropping exercise using his .300 Winchester loaded with 180s. The range was short, and he essentially walked amongst the herd dumping the designated animals. He could have used his .44 belt gun doing it like that, although he was required to make neck shots only, which with an animal of that size is tricky as the location of the spine can be deceiving due to the thickness of the neck.