A look at a bear distribution map says your route will have at least black bears almost the entire way.
If you look at bear distribution maps for Canada you will see there are bears even in NS and NB.
I started out in Halifax, NS a few times. I would ask the local people for the bears, but they would say there are no bears in NS. Maybe if you go to the deep deep hinterland of NB, otherwise not. So one thing is what a map says - another what locals tell you.
When I reach the Rockies I will take my precautions because I KNOW there are bears for sure - I have seen them several times. To me it is a mental stress to set up camp earlier, finding a tree for hanging food, finding a bear container, assesing the situation of wind direction, looking for rivers and streams, observing all kinds of distance rules etc etc (usually only applies for wild/stealth camping). So when I did the NT, I passed through LARGE areas of bear populated areas in the east, but never saw a bear and the locals told me there are no bears. Doing the NT again I would not bring a bear spray at all and worry about food hanging until I reach the Rockies. So what I would basically do is ramp up my precaution level when I reach the Rockies (if doing the NT). But on the roads in Ontario and Quebec I have no idea what the real situation is: Do I need to take Rocky Mountain like precautions already there?