Be patient. Bears will hang up and study the bait sight. Once they commit, they are yours. Biggest problem alot of people do is get too eager to get bow in hand and scare the bears. They will come in. When they do....you normally have time to study, and wait for perfect shot.
If the bear looks big....it is big. Too many people say look at the ear size, etc. I found out that bears are all different. If the first thought is that it looks small, wait. If you think it is big, it prolly is. Not too different then deer hunting.....if you have to study the deer, it prolly isn't as big as you think for the most part. Bears are no different.
My first bear hunt was in Ontario and I saw 2 bears before I shot mine. The bears I saw were tiny and I thought so. When I saw the bear I shot.....there was no looking and only waited for the shot.
Hopefully this helps out. This is just what I found out hunting bears in WI where we now have more bear in the north woods than deer. haha