WASHINGTON - Seven Canadian premiers wrapped up a three-day visit to the U.S. capital Sunday, some of them heralding a new era in Canada-U.S. relations following their moment in the spotlight at an influential conference of American governors.

The premiers of Ontario, Quebec, Manitoba, Saskatchewan, Nova Scotia, New Brunswick and Prince Edward Island were warmly welcomed by U.S. power brokers throughout their time in D.C., including by three top-level figures in President Barack Obama's administration.

But the highlight of their trip was their participation in the winter meeting of the National Governors Association, with about 20 U.S. governors, mostly from border states, joining them for a round table entitled "Common Border, Common Ground."

The goodwill was in such abundance that Pennsylvania's Edward Rendell was easily nudged to warble a chorus of "O Canada" after he was overheard boasting to his Michigan colleague, Jennifer Granholm, that he knew the words.

"I've turned what I think are the best lyrics into one verse. I can't sing; I sound like a sick squirrel, but I will try my best," Rendell said before raspily launching into an almost-accurate rendition as Canadian reporters cheered him on.

Mississippi Gov. Haley Barbour raved about the relationship between the two countries.

"The Canadians are not just our closest neighbours, they're our best friends," he said. "There's hardly any place in the world where you could have an open border of this distance. It's breathtaking; what a wonderful relationship."

Official business ended Sunday as the premiers sat down with Obama's agriculture secretary, the third high-level administration official to meet with them in as many days.

On Friday, they met at the White House with his economics czar, Larry Summers, and Lisa Jackson, the head of the Environmental Protection Agency. They raised concerns with Jackson that Canadian manufacturers might be subject to punitive U.S. measures now that the EPA has warned it will start regulating carbon emissions.

The EPA made the threat in the absence of greenhouse gas laws from Congress. That legislation is stalled due to the Democrats' recent loss of their filibuster-proof majority in the Senate with the election of a Republican to the late Ted Kennedy's Massachusetts seat.

Despite all the good will on display toward Canada during the premiers' visit, there are fears that Canadian manufacturers and energy providers who produce carbon-intensive goods will suffer under tough EPA regulations, something that is shaping up to be a hot spot in Canada-U.S. trade relations.

America's controversial country-of-origin labelling by the U.S. was the dominant topic of discussion between Agriculture Secretary Tom Vilsack and the premiers during the meeting on a brilliantly sunny morning in the U.S. capital. Canada and Mexico have complained to the World Trade Organization about the measures, saying they violate NAFTA.

Later Sunday, Ambassador Gary Doer was hosting a reception at the Canadian Embassy for governors, premiers and their staff to watch the Canada-U.S. Olympic hockey game. PEI's Robert Ghiz was among the premiers slated to take in the game.

At the roundtable on Saturday, premiers and governors alike weighed in to discuss issues of mutual concern between the U.S. and Canada that included efforts to clean up the Great Lakes, the need for free and easy trade between both countries and the prospect of Canadian oil being subjected to restrictions from the Environmental Protection Agency.

"There is a very large need for Canadian crude in Minnesota," said Gov. Tim Pawlenty, who's considered a Republican bright light and someone who will likely make a run for the party's presidential nomination in 2012.

He added that any move to penalize Canadian oil producers "is very ill-advised from my standpoint."

Granholm thanked Ontario for its help in battling the invasive Asian carp that is threatening Great Lakes ecosystems. Wisconsin Gov. Jim Doyle discussed efforts to clean up the lakes, calling it an "enormous undertaking."

"It seems to me critical that we are involved with the Canadian provinces in that so that we get the most bang for the dollar," he said.

There was nary a sign of any support for the controversial Buy American trade policies that have caused tension between the U.S. and Canada for the past year.

In his remarks at the roundtable, Ontario Premier Dalton McGuinty urged the governors to push for barrier-free trade between the two countries.

"We need to not only protect that trading relationship, we need to enhance it," he said, adding he was happy to hear the Obama administration intends to double exports in an attempt to pull the U.S. economy out of an enduring recession.

"I just want you to know, we're in," McGuinty said to laughter.

Following the roundtable, the Ontario premier said powerful Americans are now listening with an open mind to Canadian concerns.

He cited the two high-level meetings Friday with Summers and Jackson. The Summers meeting, McGuinty pointed out, ran longer than what was originally scheduled as they discussed the economic recovery.

"Those are departures, certainly from the recent president, and I think they bode well for us," McGuinty said.

He added he was heartened by the answers he received when asking throughout his time in D.C.: "Where is the protectionist sentiment going to go, how is that going to evolve?"

"And I have been reassured that while it always has some seductive appeal, there is a new awareness that in an era of globalization, where we are all so trade-dependent, that we've got to guard against protectionism and ensure we keep our trade linkages strong."

Earlier Saturday, Manitoba Premier Greg Selinger echoed McGuinty, saying he'd noticed a new tone of understanding coming from the United States.

"There's a real willingness to solve problems. I think there's a greater recognition of the value of the relationship between Canada and the United States," he said, crediting David Jacobson, the U.S. ambassador to Canada who's a close Obama associate, for his efforts to get to know the country and its premiers.

"Obviously we want to maintain our identity, our culture and our traditions but on the economic level, I think we see that we have common interests that we need to further."

New Brunswick Premier Shawn Graham described Saturday's events as an important moment in contemporary Canada-U.S. relations.

"It was a huge step forward," he said.

"Often we rely on our federal governments to work on issues of national concern, but ultimately it's at the state level and provincial level where a lot of work is done on the ground, and that's why today you saw such a love-in, because here were governors and premiers who work on a quite regular basis on a number of files and actually get the job done."

The National Governors Association conferences often help to set policy for both the White House and Congress. Health care was a dominant issue of discussion at the winter meetings, with First Lady Michelle Obama on hand earlier Saturday urging the governors to help her in her efforts to combat childhood obesity in the U.S.

The premiers were in D.C. for the first-ever meeting between the association and its Canadian counterpart, the Council of the Federation.