"The sketch was conceived when SCTV moved to the CBC television network. Due to the difference in the amount of time allocated for commercials, each episode to be broadcast on that network was two minutes longer than those syndicated to the United States. The CBC network heads asked the show's producers to add specifically identifiably Canadian content for those two minutes. Rick Moranis and Dave Thomas thought that this was a ridiculous request, since the show had been taped in Canada, with a mostly Canadian cast and crew, for two years. The request inspired them to create a parody that would incorporate every aspect of the humorous stereotype of Canadians."
-- from the Wikipedia entry for SCTV's Bob & Doug McKenzie