From the Argo Wikipedia page
Canadian vs. CIA roles
After the film was previewed at the Toronto International Film Festival in September 2012, some critics said that it unfairly glorified the role of the CIA and minimized the role of the Canadian government, particularly that of Ambassador Taylor, in the extraction operation. Macleans asserted that "the movie rewrites history at Canada's expense, making Hollywood and the CIA the saga's heroic saviours while Taylor is demoted to a kindly concierge." The postscript text said that the CIA let Taylor take the credit for political purposes, which some critics thought implied that he did not deserve the accolades he received. Affleck changed the postscript text to read, "The involvement of the CIA complemented efforts of the Canadian embassy to free the six held in Tehran. To this day the story stands as an enduring model of international co-operation between governments." The Toronto Star complained, "Even that hardly does Canada justice." When interviewed, Taylor noted that, "In reality, Canada was responsible for the six and the CIA was a junior partner. But I realize this is a movie and you have to keep the audience on the edge of their seats." Taylor is also shown threatening to close the Canadian embassy in the movie; in reality, this never happened.
"Because we say it's based on a true story, rather than this is a true story, we're allowed to take some dramatic license. There's a spirit of truth", and that, "the kinds of things that are really important to be true are—for example, the relationship between the U.S. and Canada. The U.S. stood up collectively as a nation and said, ‘We like you, we appreciate you, we respect you, and we’re in your debt.’...There were folks who didn’t want to stick their necks out and the Canadians did. They said, ‘We’ll risk our diplomatic standing, our lives, by harbouring six Americans because it’s the right thing to do.’ Because of that, their lives were saved."
What you say is true, but remember that the primary goal of Hollywood's products are to entertain, not necessarily tell the truth, the whole truth, so help you god. The percentage of "historically based" films that don't paint the whole picture or fudge some details is probably 99-100%, so this is nothing new.
As an American I was very moved by the film and by the story in general. I can assure you that Canadian government's aid came across as very integral to the plot and the survival of the six Americans, regardless of the details. Now that the movie is out, I'm sure all Americans who see it have an appreciation for the sacrifices Canada made and feel grateful for our northern neighbors.
EDIT: ps. According to the "Canadian Caper" wiki, there is already a film, released in 1981, depicting the rescue from Canada's perspective. It's called "Escape from Iran: The Canadian Caper". I might check this one out.