Your 100 to 400 will be your best all around lens. I would also take the 70 to 200 because the f2.8 will serve you well. Lots of time, the largest bears will expose themselves at the end of the day and every extra f stop of light is a blessing.
Often when you see bears they can be working up the river towards you, and you start with all the telephoto you have, and end up zoomed way in. That's when the 100 to 400 earns its keep. As a third lens, if possible, I'd take the 24 to 105, even if it meant leaving an extender at home.
Would be interested in knowing where in BC you are headed.I spend a fair amount of time looking for bears in Canada myself. There are some viewing stations in BC set up just for people to view bears, and I have had much fun at a couple of those, one near Bella Coola and another In Hyder AK, which is accessed through Stewart, BC. Have had a 20 plus grizzly day in BC and a couple 20 plus black bear days. Good luck!