Speaker of the House of Representatives Nancy Pelosi is meeting with both promoters and critics of Western Canada's controversial oilsands development, during a trip to Ottawa this week.

Pelosi, who is considered one of the most powerful politicians on Capitol Hill and has a track record of voting in favour of environmentally friendly legislation, met with Canada's environment minister and the premiers of Alberta, Saskatchewan and Quebec on Wednesday evening.

Sources who attended the meeting told CTV News that Pelosi appeared knowledgeable about the oilsands and expressed serious concerns about them.

Alberta Premier Ed Stelmach said he would use his meeting to "appeal to her sense of reason, to communicate very clearly that we continue to be focused on environmental improvement in developing the oilsands," he said on Tuesday.

"Environment is the first and most important issue," Stelmach said, adding that he plans to remind Pelosi that Canada is the largest supplier of energy into the U.S.

Alberta officials have met with U.S. politicians before, and the provincial government has an office in Washington to lobby U.S. officials on the province's oil and gas industry. But Pelosi's visit marks the first time that Alberta officials will meet her.

But as the oilsands have expanded, so too has controversy about their environmental impacts and potential health effects -- something underscored by anti-oilsands protest that took place in Ottawa as the veteran Democrat arrived earlier on Wednesday.

Pelosi will meet with environmental and First Nations groups on Thursday, and they're expected to paint a less rosy picture of the oilsands.

One of those groups is Environmental Defence, whose executive director, Rick Smith, took issue with Stelmach's characterization of the oilsands, saying that the premier "owes Canadians an apology" for "pretending that there's any environmental concern in the tarsands industry within the ranks of the Alberta government."

Smith alluded to the latest in a line of reports that suggest the environmental impact of the oilsands may be much more severe than government or industry estimates indicate.

Representatives from Environmental Defence plan to tell Pelosi "that the customer is always right, that very clearly this is an industry, this is a provincial government that are not going to move on these issues unless they're pushed."

"We're very much hoping that, as the tarsands industry harbours this ambition of dramatic growth into the United States, the U.S. government takes advantage of that position to say, ‘Look, you can't continue with business as usual -- you have to seriously address dramatic reduction in your pollution levels,'" Smith said.

Saskatchewan Premier Brad Wall and Quebec Premier Jean Charest also attended the Wednesday evening meeting.

Wall told CTV's Power Play that Canadian officials need to drive home that jobs in the U.S. as well as Canada are tied up in development plans for the oilsands -- including of a proposed pipeline that would feed the U.S. market.

"If the sabres of protectionism are rattled, or even heaven-forbid drawn, this has an impact on jobs in America, much as it does in Canada," he said. "This is a point we have to make."

While Saskatchewan currently has no commercial oilsands projects, Wall said that the province has about 10,000 square kilometres of land that could be exploited for that purpose.

He said he also plans to address the use of environmental technologies such as carbon sequestration to minimize the environmental affects of extracting so-called "heavy oil" when he meets with Pelosi.

With files from The Canadian Press