sure, there are bear attcks. you can read about every one of them in north america here:
List of fatal bear attacks in North America - Wikipedia, the free encyclopedia
almost all of these are attacks against lone people or pairs, some from pets or trained animals, and a couple in incidents where the urban sprawl and nature are bumping up aginast each other. most are in yukon, alaska and bc, where grizzlies are much more aggressive.
that's 32 total attacks in all of north america (3 in ontario) in 20 years. if you are travelling in a group in a well-travelled area this is simply not something to be worried about.