The following is quote from a September 9, 2004 joint letter - posted on mcleans.ca web-site:
"As leaders of the opposition parties, we are well aware that, given the Liberal minority government, you could be asked by the Prime Minister to dissolve the 38th Parliament at any time should the House of Commons fail to support some part of the government’s program. We respectfully point out that the opposition parties, who together constitute a majority in the House, have been in close consultation. We believe that, should a request for dissolution arise this should give you cause, as constitutional practice has determined, to consult the opposition leaders and consider all of your options before exercising your constitutional authority. Your attention to this matter is appreciated."
-From a letter to then-Governor General Adrienne Clarkson signed by all three opposition leaders: Gilles Duceppe, Jack Layton and Stephen Harper (September 9, 2004)
Harper also did a wide ranging interview (at the time) with CBC's Evan Solomon wherein he said:
"Harper: Well there are lots of things that could bring the government down, but my opposition can not bring the government down. The government can only be brought down because it alienates several parties in the House. And the first obligation in this Parliament, if the government wants to govern, it has to come to Parliament and it has to show that it can get the support of the majority of members, through the Throne Speech, through legislation, and through budget and supply, and the government to this point has made no effort to do that, but that's its first obligation."
Does he operate by a different set of rules when he's P.M. rather than when he's the Leader of the Opposition?