Perhaps Dave Barrett losing in 1993?
Also Dave Barrett losing in 1975 to some anonymous Social Credit car dealer. (I think George Kerster was his name.) If I recall correctly, the story was somewhat strange in that the Social Credit nominee was originally going to be the brother of the person who was ultimately nominated.
Much bigger though was New Democrat Margaret Mitchell losing to Liberal Anna Terrana in Vancouver East in 1993. Vancouver East is probably the safest of the few safe seats that the Federal NDP have in the entire country. (Right now I'd say the two Windsor ridings are the next safest.)
Others:
Saskatchewan NDP Attorney General Roy Romanow in 1982 losing to some anonymous young (I think 19 years old) gas station attendent. Romanow also lost by around 19 votes. That entire general election result was a massive surprise.
Not an incumbent at the time, but Progressive Conservative Party leader (and briefly former Prime Minister) Arthur Meighen losing to anonymous high school history teacher New Democrat Joe Noseworthy in a 1942 by-election in York South.
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I wouldn't consider the 2004 election result in North Vancouver to be an enormous upset. The Federal Liberal Party also had some historic strength in North Vancouver (not enough to win but the NDP was basically non existent in the riding, so it was a two party race) and their candidate was the popular mayor of the District of North Vancouver, Don Bell. The incumbent Conservative M.P, Ted White, although generally regarded as a nice guy, was also fairly flaky.
