The National Bank of Canada is the 6th major domestic bank in Canada. While it isn't as large and doesn't have the reach (especially internationally) the others have, it is a major player in Quebec (where 475 of its 655 branches are located), and has growing investment, corporate banking, and insurance divisions.
National's place in the (presumably) impending consolidation of the Canadian banking industry is murky. Currently (because of its small size) there are no restrictions preventing one of the other banks from buying it up, but the government of Quebec (through it's powerful Caisse de dépôt et placement du Québec) would likely block such a move, since the National is the last major bank still based in Quebec. The Quebec government, it is presumed, would like a major European (preferably French) bank to buy the National, but leave it intact as a separate unit headquartered in Quebec.
National Bank of Canada website - http://www.nbc.ca