Canwest News Service: The Sierra Club is hoping to use the upcoming visit of U.S. President Barack Obama to deter the United States from supporting the Alberta oilsands as a viable energy source. By launching a new website, circulating a petition and hosting a film festival with a focus on the environmental group’s concerns, the Sierra Club hopes it will be enough to keep Obama’s goals of cleaner energy intact by staying away from the oilsands. “In short, the message is, ‘Don’t buy our dirty oil,'” …