It's the end of an era for Canada's most important diplomatic post as Gary Doer confirmed Monday that his longer-than-usual stint as ambassador to the United States is about to conclude.

The popular former premier said he'll help prepare the transition to a new Liberal government and will leave it to the incoming government to pick the specific departure date.

Rumours about his impending departure had been swirling for months given that his six-year D.C. stint had already lasted longer than his last two predecessors combined.

The sports-loving ambassador had always sidestepped those rumours in characteristic fashion: with a joke about hockey. He used the same metaphor Monday to announce the final siren.

"I've said informally around Washington ... I'm in double overtime, and am not going to go into triple-overtime," Doer said in an interview next to his office, overlooking the U.S. Capitol.

"I've made that very clear — before the election, during the election, after the election. I'm participating now in the orderly transition that takes place obviously between the outgoing and the incoming government."

As for the specific departure date: "The day is not confirmed," he said. "There was a desire, administratively, to have a

transition (period)."

The former NDP premier of Manitoba was appointed by Prime Minister Stephen Harper in the hope that his left-of-centre roots and social network might help relations with the then-rookie Obama administration.

Keystone, border and TPP among key files

Much of the media chatter in the last six years has focused on one irritant: the stalled Keystone XL pipeline, which both Harper and Doer advocated without success so far.

But the era also witnessed a series of major Canadian priorities coming to fruition.

They include:

A sweeping arrangement that would change the way Canadians and Americans cross the border, creating customs points away from the border with the goal of faster crossings. To take effect, the deal must be approved in Parliament and Congress.

Canada's entry into the Trans-Pacific Partnership trade negotiations, which happened after considerable lobbying of U.S. politicians and stakeholders. Negotiators finally reached a deal this month, although that too faces implementation debate in legislatures.

An agreement on a new Detroit-Windsor bridge that bypassed a blockage in the U.S. Congress. Canada will finance the bridge, and also collect tolls on what will become the most important border crossing.

Anti-red-tape measures, with the negotiation of harmonization of rules for a wide range of products.

A coveted classification for Canadian hydro as a renewable energy, which could increase exports from Quebec, Ontario, Newfoundland, B.C. and Manitoba.

Future up in air

Speaking of Manitoba, Doer all but confirmed that's where he's headed next: "I've never sold my home in Winnipeg," he said. "Winnipeg's always been my home. I didn't sell my house, I didn't sell my cabin."

He declined to say what his future plans are. Doer said they will likely involve some Canada-U.S. issues, but he avoided delving into details. He also declined to discuss specific policy issues, given the transition-time caretaker rules about public comments by government employees.

"I don't want to go into much more detail," Doer said. "I'll talk about the future when the future starts — which is not quite yet ... I loved being premier. It was an honour to be an ambassador. It's always an honour to represent Canada."

Ambassador Bob Rae?

There's been speculation for months about who might succeed Doer, with embassy staff hearing different names about his potential replacement based on who might win the election.

With the Liberals in power, some of that attention has turned to another former NDP premier -- this one spent part of his childhood in Washington as the son of a diplomat, and he went on to temporarily lead the federal Liberals: Bob Rae.

Former Liberal interim party leader Bob Rae, and veteran politician, has been floated as a potential candidate for Canada's top diplomatic posting in Washington, D.C. THE CANADIAN PRESS/Sean Kilpatrick (Sean Kilpatrick/ Canadian Press)

Insiders at the embassy, and in Ottawa, have mentioned Rae as a possible candidate for one of two high-profile diplomatic posts: a replacement for Doer, or for the United Nations ambassadorship in New York.

Rae wouldn't touch either of those rumours Monday. But he did agree to speak about Doer, whom he's known for decades and called an outstanding premier and ambassador.

He said Canadians were well served by Doer's sharp political instincts, and deep contacts in different parts of the complex U.S. political machine that includes both parties in Congress and state governors.

"You only have to talk to Gary for five minutes on any subject to understand he's very well-informed. He has tremendous personal contacts," Rae said in an interview.

"I can't think of anybody who has a better ability to chat with people, with disarming candour. Very approachable. Huge amounts of charm. And a tremendous amount of knowledge about any file he's working on."

Rae said there have been some missed opportunities in Canada-U.S. relations in recent years, but that the blame doesn't belong exclusively to any country or political party.

He said he hopes to see deeper co-operation on climate change and energy between all three North American countries — the idea is already supported by the next Liberal government, and by Democratic frontrunner Hillary Clinton.