The Liberals are expected to keep dominating urban, 416 Toronto but the potential for electoral drama looks to be much greater in the 905 belt of the GTA.

That could explain why Conservative Leader Stephen Harper will make a Tuesday night rally in Mississauga his first GTA stop of this federal election campaign. Liberal Leader Stephane Dion will be in Pickering, visiting the headquarters of local Liberal incumbent Mark Holland.

The Strategic Counsel polling firm has identified four of its 45 national battleground ridings-- ridings with narrow margins of victory in 2006, where shifts could occur that will affect who forms the government -- in the GTA.

The region, which stretches from Burlington to Oshawa, includes the following "battlegrounds:"

• Burlington
• Halton
• Mississauga South
• Oakville

Halton is one riding the Tories would love to win above all others. Why? Two words -- Garth Turner, who got punted from the Tory caucus then joined the Liberals about four months later.

Turner took the riding for the Tories from Liberal Gary Carr in 2006 by about 1,900 votes. But he ran afoul of Harper and his caucus mates, allegedly through indiscreet blogging.

"We have a long history of defeating Conservative turncoats," Will Stewart, president of the Halton Conservative Association, told ctvtoronto.ca on Monday -- a reference to the fact that Carr had once been a provincial Tory cabinet minister.

Lisa Raitt, CEO of the Toronto Port Authority, will carry the Tory banner against Turner in the affluent riding. She was handpicked by the national office.

On his blog, Turner wrote last week: "I am hoping the people I have represented will prove with their votes that a guy like me can actually survive in this system."

The Oakville riding, which voted Tory in the Mulroney era, shares a boundary with Halton. In 2006, incumbent Liberal Bonnie Brown got a scare from Tory Terence Young, winning by fewer than 800 votes. Young will be her main opponent once again.

Oakville sits southwest of Mississauga South. Paul Szabo won that riding for the Liberals with a 2,100-vote margin over the Tories. Szabo has held the riding since 1993, but it was Tory blue from 1979 to that year.

Burlington sits to the southwest of Oakville, meaning the four ridings are somewhat clustered. The Tories captured Burlington in 2006, with Mike Wallace defeating four-term Liberal incumbent Paddy Tornsey by about 2,600 votes. Burlington had been a Tory riding from 1979 to 1993.

In Burlington, a "united left" vote would have defeated the Tories by almost 9,000 votes.

'Spite' ridings

Three other ridings to watch for fun over their possible spite value, meaning mean-spirited partisans would particularly like to see the riding change hands, are:

• Newmarket-Aurora
• Whitby-Oshawa
• Mississauga-Streetsville

The latter is the home of Wajid Khan, who was re-elected as a Liberal in 2006 and defeated his Conservative challenger by about 5,800 votes. But after serving as a special envoy for Prime Minister Stephen Harper to the Middle East and Pakistan, Khan jumped to the Tories in January 2007.

Consultant Bonnie Crombie will carry the Liberal banner against Khan.

Belinda Stronach isn't running this time in Newmarket-Aurora. First elected as a Conservative in 2004, the one-time Tory leadership candidate shocked the political chattering classes into silence in 2005 when she jumped parties after a tiff with Harper, helping save the minority Liberal government of Paul Martin.

The daughter of billionaire auto parts magnate Frank Stronach won re-election as a Liberal in 2006, but after it became apparent she wouldn't have a substantial role to play after Stephane Dion became party leader.

In Whitby-Oshawa, one of Finance Minister Jim Flaherty's most aggressive critics wants to unseat him.

Brent Fullard has never forgiven the Conservatives for reversing a 2006 campaign promise not to tax income trusts. That policy shift cost Canadians about $25 billion.

"I'm not seeking to run for the Liberals in (any) riding, I'm seeking to confront Flaherty on his policies and his competence for office. And I can't do that anywhere else but Whitby-Oshawa," the founder of the Canadian Association of Income Trust Investors said Sunday.

The riding's Liberal nomination meeting is Tuesday.

The auto industry -- particularly General Motors -- is a key employer in and around Flaherty's riding. The Tories reached an election-eve deal last Friday with General Motors to build a hybrid car in Oshawa and invest $245 million in a plant in St. Catharines in exchange for forgiving a $200-million loan.

Flaherty took his riding by about 3,500 votes, but fellow Tory Rick Dykstra only eked out a 246-vote victory in St. Catharines over incumbent Liberal Walt Lastewka, who will attempt a comeback.

A changing region

Regionally, the Liberals hold 15 seats in the 905 belt and the Tories four. The NDP's highest-profile candidate in the region, former union leader Sid Ryan, faltered in Oshawa in 2006. The social democratic party currently has no MPs in the wider GTA.

Provincially, the Progressive Conservatives of Mike Harris enjoyed success in outer suburbia and many think that would be an area where the federal Tories could also make gains, especially since they have previously held these areas when they were governing.

But "demographically, (the ridings) have changed. They're not so white bread any more. They're much more diverse," Peter Donolo of The Strategic Counsel told ctvtoronto.ca. "They have a greater comfort level with the Liberal brand, and they're concerned about the baggage Harper carries from the Reform party and Alliance."

The big factors for the Tories in making gains will depend on how much they are seen to shed that baggage and how much the election turns on "lunch-bucket" issues such as the economy and taxes, he said.