From top to bottom are Wilfred Laurier, John A. McDonald, Queen Elizabeth II, William Lyon Mackenzie King, and Robert Borden. They're all important figures in the history of Canada -- all Canadians learn the names in school, but I'm not sure how many actually recognize or remember.
I thought that the names belonging to the faces were on the bills, which makes it kind of easy. I pulled a $20 out of my pocket to confirm this, but was unable to see it. As it turns out, the name is on every bill except the $20 -- it seems whoever designed our modern currency assumed that everyone would recognize the Queen.
Regarding what these people are famous for -- with one obvious exception they're all former Prime Ministers of varying degrees of importance. Wilfred Laurier was the first French PM, John A. McDonald was the first PM after the BNA Act, the Queen is the Queen, Mackenzie King was PM during the second world war and Robert Borden was PM during the first world war.
As with all of the commonwealth nations I think, the Queen is on all of our coins.