First, of course the US did not want Canada to leave Kandahar in July 2011. For one thing, the Canadians have proven to be among the most reliable and effective troops in Afghanistan. That may or may not be saying that much, given how many other countries have not been willing to deploy to the hardest parts of Afghanistan. Moreover, it is one thing for the Dutch to leave since they had a government fall over this issue, but it is another thing for a stalwart ally like Canada to be an early departer. So, the US didn't want the Canadians start a stampede towards the door. So, no one but no one should be surprised the US wanted Canada to stay. Even so, I remember op-eds and letters to the editor over the past couple of years with Canadians being upset that the US was asking the Canadians to stick around. They should have taken it as a compliment.
Second, the articles on this "news" seem to suggest that Harper was being two-faced with the Canadian people--that he was saying no to anymore combat to the public but thinking about it in conversations with the Americans. Given the outcome, a non-combat mission in relatively safer parts of Afghanistan, it should be pretty clear that Harper was more honest with the Canadians than the Americans.
His comments appeared to give hope to U.S. officials that "the minority government of Prime Minister Harper may not have actually ruled out extending Canada's 2,800-member military contingent, including combat forces, in Kandahar beyond 2011."This gets to the larger points about wikileaks: (a) governments will soft-pedal their resistance to requests so that the relationships are not damaged; (b) the US diplomats reporting stuff back home may be wrong. Harper told the Americans that he would think about it--that is hardly a commitment of any kind. It was a way to put off the Americans without making any kind of commitment at all. The Americans, guilty of wishful thinking, sent back reports that suggested that the Canadians would change their minds. They should have (and probably did) sent back reports observing that domestic dynamics and Harper's lack of enthusiasm for the mission would make an extension highly unlikely. Indeed, wikileaks does not put out a complete set of cables--just those that would be most embarrassing. So, the ones where the US diplomats accurately gauge the Canadian stance have not been released, if they exist.
Which gets to a larger point--if this is the kind of stuff that they think is most embarrassing and potentially harmful to the relationship (since that does seem to be the goal of wikileaks--to sow discord), then US-Canadian relations are pretty healthy. If this "controversy" is the best they got, then perhaps US-Canadian relations are extremely boring. Not a bad thing.