MONTREAL -- A former Canadian ambassador says he's less confident now than he was a few years ago about the U.S. giving the Keystone XL pipeline project the green light.

"Two years ago I was very confident that it would be a positive reaction, a "Yes" would come," Raymond Chretien said Wednesday.

"Recently, I'm beginning to see signs that lead me to believe that a "No" is possible."

Chretien made his comments during a chat with U.S. Ambassador Bruce Heyman at a luncheon speech.

The event was organized by the Montreal Council on Foreign Relations.

Chretien pointed to a recent announcement by the Obama administration to back up his remarks.

In early June, the United States announced its most aggressive climate-change measures.

The regulations would chop carbon emissions from U.S. power plants by 30 per cent by 2030, with the majority of those cuts coming by the end of this decade.

"When your president announced those measures on coal, clearly it's a legacy issue for him," Chretien told Heyman, "He wants to go down in the history books of his country as a green president."

The former Canadian ambassador admitted he's worried about the future of the proposed Alberta-to-Texas pipeline.

"I would tell our government: 'listen, a "No" is possible, let's get ready with a very good Plan B, let's get moving,"' Chretien said.

During his remarks, Heyman said Obama is really focused on "leaving the planet in a better place than it is today."

The U.S. ambassador added that the Keystone pipeline project "is a very serious issue" for Canadians -- and Americans.

He recalled that since the beginning of the year, more than three million comments have been received from the public in various forms including emails and letters.

But they still have to be analyzed and "you have an obligation to read those."

"This is a huge task for us to do, it's going to require additional time, we don't have a department of memo reading in the state department," Heyman added.

When asked later by reporters whether the comments were positive or negative, Heyman would only say there was a very wide spectrum of comments.

"We see a strong environmental message," he said, quickly adding that the public comments included everything that could be imagined.

Chretien served as Canadian ambassador in Washington from 1994 to 2000.