The movie Argo is notoriously inaccurate, like its silly ending chase scene. But I was wondering if the movie guys had a reason to explicitly portray the Canadians as getting the credit for the rescue while only playing a supporting role. What do we know?
Actually, the movie was inaccurate in the way it downplayed the Canadian Governments role in the rescue, not the other way around.
The Canadian Ambassador to Iran, Ken Taylor, initially proposed the plan of getting the six Americans out of Iran using Canadian passports to Canadian Prime Minister, Joe Clark, and the Secretary of State for External Affairs, Flora MacDonald. The CIA only assisted with the operation by creating forged Iranian Visas to be used in conjunction with the Canadian passports (that were officially issued by the Canadian Government per an Order in Council) as well as sending Tony Mendez along with the cover story (the Argo film production) used to shepherd the six diplomats safely out of Iran.
The movie also ignores that the British, did actually house the six Americans for a night, but later moved them to the Canadian's facilities as they figured it would be more practical and safer for the six. So the line about the British and New Zealand Embassy's turning away the Americans isn't very accurate either.
I will say the one thing the movie does do reasonably well, is the beginning scene showing the storming of the American Embassy. While they obviously compressed an event that unfolded over a couple hours into a shorter time frame, they did make the important distinction in showing that the role of the Marines and DSS staff at the embassy was to merely buy time to allow the Embassy Personal to destroy sensitive documents and communications equipment, not to start opening fire on the protesters or use lethal force to prevent the embassy being overrun (which would have likely resulted in many of the Embassy personal being killed in retaliation or further violence).