For Canada, I'd say arguably the disastrous raid at Dieppe. http://users.pandora.be/dave.depickere/Text/dieppe.html
For my "other" country, Newfoundland (independent until 1949, when Canada joined it), it would be the same as Doppelganger's reply, as the Newfoundlanders were attached to the British. In Newfoundland's case, the two most pointed examples would be Gallipoli and Beaumont Hamel (the Somme offensive).
\"What are you talking about? One, two, three, fo-- oh, crap.\"
- G. Edwin Bergstrom, Arlington VA, 15 Jan 1943