OP I have hunted them free range in Alberta (near Wood Buffalo National Park) and in the Northwest Territories. It is a great hunt for real wild bison in those areas and as Brickburn said, it is a lot of work getting a big bull out of the middle of nowhere. Hunts in those areas are typically in the winter as that is the only time you can access some of that country. Long hours on snow machines in -30 or so, covering a lot of wilderness with help a LONG ways away. The Alberta hunt can be done DIY, the NWT you have to use an outfitter. There are also some outfitters who do hunts in northern Alberta for the bison near Wood Buffalo.
There are also one or two outfitters in British Columbia that have an allocation for wild plains bison up in the NE off the Alaska Hwy in the Pink Mountain/Sikinni River area. Additionally there are outfitted hunts for wood bison available in the Yukon.
I know guys who have done the Custer State Park hunt and it is pretty much a cake walk. They are no more wild in that park than on most big bison farms. The hunts is done from a pickup truck and there is a crew to come in and retrieve the animal once it is shot.
I have also talked to a few who have drawn in Utah and from what I have been told the Antelope Island hunt is again, a cake walk, if you want a real hunt you should focus on the Henry Mountains.
Alaska offer some good bison hunts through a draw. The better areas are fly-in and you are going to work hard.
I am not familiar with all of the MT and WY hunts, but I do know that some are very easy and others are more of a hunt, so you would have to do your research.
Cheers!