To the OP I would suggest a trip to Elk Island park. Go have a look around maybe jot down the types and numbers of animals you see then come back and let us know if the bison are a real danger to the elk and moose in the area.
Scientists say that at one time they were the largest herds to ever roam the earth. (60 million strong)
There are herds in the Yukon, northern BC, Northwest Territories and Alberta. The only ones with the Brucelosis/tuberculosis are the Wood Buffalo park and they are kept from intermingling with the northern and western herds using Bison control areas.
In the past couple of years there has been a controlled hunt of them in Northern Alberta as some of our smiling friends her on AO would be happy to show you pictures of.
Will there be problems with a reintroduction of bison in Banff? Of course there will. Just how many problems and how often a person can't really say. But I'm sure there will be run ins with ranchers and tourists like the one shown in the video already posted. By far the biggest danger will be vehicle collisions.
Here in the NWT we don't have all of the ranching issues to deal with, but we do have Bison and some get hit every year.
http://drivealive.ca/driving-north/s...son-awareness/
I guess to me I look at it this way. They were here before any of us, our native brothers included. Do we really have the right to dictate what species can be included in the natural environment? Men have always done this but that doesn't necessarily make it right.
Will they attract predators? Yes. Will that be detrimental to the elk/moose/deer/sheep? Maybe, maybe not. Time would be the judge of that. There seems to be more predators around these days anyways, except of course grizzly bears which are extinct in Alberta (everyone knows that)
Personally I love having the Bison around. I like the majesty of them and just how tough they really are, and they make great burger .....lots and lots of great burger.
So I say let a few go and see what happens maybe it will be a disaster, maybe a win/win for everyone involved. Take your kids and show them, tell them how there used to be millions of them. They'll love it, there aren't too many animals more impressive than a giant bull Bison just doing what he does.