Bears are beautiful animals that must be respected.
Adult bears are usually bigger, stronger and faster than humans. Those that aren't (cubs), are often accompanied by one that is (mother).
Don't ever get between a bear cub and the mother. Mother bears are very protective and will take you out if necessary - her decision - not yours!
Bears have good eyesight and hearing and an excellent sense of smell.
They are good climbers and strong swimmers, so a tree or an island may not provide refuge.
Most bear encounters happen along a portage or in camp. Check with the local park authorities to find out about recent bear activity before you leave on your trip. Most parks that contain active bears will also have some suggestions on how you should behave.
Statistically, you are in greater danger of being grievously harmed by bees, your family pet or lightning, than by bears.
The bottom line is to avoid a confrontation, if at all possible.
A Bear - Free Campsite:
Check each campsite for bear scat. If it is relatively fresh, consider moving on to another site.
A bear in camp has one objective - food!
Food to a bear can include cosmetics, insect repellents, toothpaste and garbage.
In order to bear proof your site, as much as possible, you will have to eliminate or move anything that will attract it.
NEVER, NEVER, EVER TAKE FOOD INTO YOUR TENT!!
Keep all food handling, cooking and consumption at least 50 metres away from your tent. This may be difficult in some areas, but you will have to judge what is safest based on the possibility of bears in that area. Hanging food bags between two trees seems to be the most common option. This should be done 50 metres away from the tent, if at all possible.
Sealine bags or olive jars, if hung properly, are good ways of preventing odours from attracting bears. As well, raccoons, porcupines, squirrels, etc. will be discouraged from sharing your food.
Dishwater should be disposed of by throwing it into the bush at least 50 metres away from camp. This allows the soil to filter out any solids. Bears like fish, so clean any that you catch away from camp, and get rid of the remains by leaving on a rock or out in the lake or river for the gulls, eagles, etc. Wash up after handling food to prevent smells transferring to your gear. Any garbage that smells like fish should be burned.
Do not bury garbage! Bears will dig it up and present problems for the next users of the campsite. Do not dispose of leftovers in the latrine, as bears will find it and destroy the latrine in the process, thus reducing a 5 star site to a 2 star in one go.
Keeping a fire going all night may deter some bears, but can be inconvenient when you have to get up several times to maintain it. Also, in well used campsites, bears may be used to it and not be put off.
If a bear does come into your campsite, don't panic! It is usually frightened off by loud noises, such as whistles or the banging of pots or paddles against trees and yelling. Don't move towards a bear. It will think that you are invading its space - not good.
If the bear is stubborn and won't leave, you should find another campsite. Discretion is the better part of valour. This latter comment is based on experience!
Along Portages:
Bears are more active at dawn and dusk. Stay on marked trails and be aware of any warnings.
Be alert and aware of your surroundings and make noise as you go. Noise will give it time to get out of your way. Bears are normally afraid of humans and will avoid a direct confrontation. If you see a bear in the distance, leave the area or try to give it wide berth. Do not approach a bear even if it does not seem to be threatening.
If a bear approaches you, do not run. If it is standing up or sniffing the air, it is trying to identify you. Make some noise and move away, while keeping it in sight.
Once in a while, a bear will false-charge, turning away at the last second. If this happens when you are in the middle of a meal, leave the area immediately. Always let the park authorities know of such an encounter. Food-conditioned bears lose their natural fear of humans and can become increasingly bold as they begin to associate people with an easy meal. Bears that become used to eating human food won't lose their taste for it and park officials, in most cases, are forced to kill them.
Food Storage
There are two schools of thought on food storage.
Hanging from trees or putting on the ground in the bush.
My preference is hanging. Hanging a food pack in a tree involves more than hauling it up a tree. Remember that bears are good climbers and will destroy a pack if only one tree is used to suspend the food.
There needs to be distance away from the tree in order to make it difficult, if not impossible, for the bear to get at the pack. Hanging should done at least 50 metres away from camp, if at all possible.

You will need about 25 metres (80 - 100 feet) of rope to do this. Decide whether you will attach the food containers to the middle before the rope goes up, or use a pulley to haul them into place after the horizontal rope is in place. In either case, a loop should be made in the middle of the rope. Toss one end of the rope over a suitable branch and secure that end of the line. The knots will have to be of a type that can be undone easily after there is considerable tension applied to them.
The other end of the rope is tossed and tied in similar fashion after attaching the food containers or pulley to the centre loop. if the food is heavy, it may be difficult to raise it to the expected level by only pulling on the ropes. Get someone to toss them up as you pull on the ropes. This will make them easier to raise.
Some adjustment may be necessary in order to centre the food between the trees, keeping in mind that at least 3 metres away from both trees is best.
Having done all this, remember that in rare cases a bear may have learned to sever the ropes without climbing the trees.
Putting food containers at ground level away from camp (at least 50 metres) in the bush is practised, with success, by many trippers. The caveat is that there must be no smell attached to these containers.
Bear Spray (Pepper Spray) is only effective in a direct confrontation with a bear. Some people have actually sprayed their campsite with the stuff, thinking that it will deter the bears. This only wastes it and waters it down to the point where bears probably enjoy it as a condiment for their repast.
The Ontario Ministry of Natural Resources page has good information on
Bears
As well, check out The North American Bear Center