There is a party who is quite upset with the American environmentalists: the Canadian government. Prime Minister Stephen Harper made the angry point that Canadian environmental matters should be decided by Canadians and not Americans. Harper went on to say that Canada was not a national park for America.
The statement signifies Canadian anger towards American attitudes towards Canada. Canadians often feel that Americans take Canada for granted, assume that there is no national difference between the two peoples, and care little for the Canadian perspective. This feeling is summed up well in Margaret Atwood's Through the One Way Mirror. Americans deciding what is best based off Canada's environment and not Canada's economy has just inflamed this already existing resentment.
This anti-Americanism could have major consequence for the United States. The pipeline helps Canada export oil from the Athabasca oil sands. The current production from those oil sands is 1.3 million barrels a day. That's slightly under the daily output of Qatar and the United Kingdom. Harper has threatened that if the United States does not work with Canada to expand the Keystone Pipeline then Canada would have no problem selling the cheap, non-terrorist funding oil to the People's Republic of China.
American attitudes towards Canada and how Canada perceives American attitudes could have a huge impact on jobs, the economy, and who gets the fuel to power their superpower country.