Sources say it appears that Natural Resources Minister Joe Oliver might step into the Finance gig, now that Flaherty has decided to resign from cabinet.
The Prime Minister's Office would not confirm Oliver's promotion, but the 73-year-old cancelled an event that he had scheduled in British Columbia for Wednesday.
Whoever Harper chooses must keep the beat on the government's single biggest refrain — strong, stable stewardship of the economy — into the election campaign set for next year.
"It is a huge loss to the extent that he has been, in many ways, the economic brand maker and brand holder for the government," said Geoff Norquay, a Conservative strategist and former senior aide to Harper.
"Everybody knows that the minister of finance works for the prime minister, but the finance minister is the one who has his or her hands on the economic tiller day in, day out, year after year."
Geography, past experience, communication skills, and the ability to get along with a leader who has strong thoughts of his own on economic policy will be just some of the factors at play.
Oliver is widely respected within the Harper cabinet and among Conservatives, and is well known on Bay Street, having spent decades working there as an investment banker. He went on to become executive director of the Ontario Securities Commission and then president of the Investment Dealers Association of Canada.
But Oliver has a much different demeanour than Flaherty, and often appears gruff and highly partisan.
The government's approach to selling the Keystone Pipeline under Oliver was first punctuated by attacks against environmental groups. Now critics, including Saskatchewan Premier Brad Wall, have been calling on Ottawa to shore up their environmental cred to win favour with Washington.
Observers noted that whoever fills Flaherty's shoes will have their work cut out for them.
"The question is, who in that cabinet actually has fiscal and economic bona fides to bring to that pivotal role?" said Liberal finance critic Scott Brison.
"It's not clear anybody has the same level of experience that Mr. Flaherty had."
John Manley once found himself in the same situation as will Flaherty's successor. The president of the Council of Chief Executives was named finance minister when Paul Martin left the post after a decade in the Jean Chretien Liberal government.
Manley dismisses the notion that any minister is irreplaceable.
"I think there was some mythology that was built up around Mr. Martin. There were lots of people who thought that it was the rock upon which the government was built," said Manley.
"I just don't think that's true of anybody. Government is big and complex and it takes a lot of players to make it work."
Manley noted that whoever replaces Flaherty will also have a stretch of time to get up to speed on the portfolio, since the next budget consultation period likely won't start until September.
The opposition, meanwhile, is keen to see who takes on the job and where that person lines up ideologically compared with Flaherty.
Flaherty is a staunch fiscal conservative who had recently questioned the advisability of a key Conservative platform promise from 2011. He suggested there were better ways of spending billions in government surpluses than on extending income splitting to couples with children.
While it's unclear Flaherty and Harper actually ever clashed on that policy point, the prime minister eventually expressed his support for income splitting following two weeks of fractious headlines. Many members in the Conservative caucus, Kenney chief among them, had said the government could not abandon the promise.
The opposition blast income splitting as poor public policy that will favour the wealthiest families, while suppressing labour force participation and doing nothing for the vast majority of Canadians — notably those in which both parents work.
"We saw around the income-splitting issue a schism in cabinet," said Brison. "People interested in progressive policy and middle class families will be watching this appointment with great interest, given that schism in cabinet around the income splitting issue."
NDP finance critic Peggy Nash said Flaherty's departure means one less voice of opposition to income splitting in the Conservative cabinet.
"Mr. Flaherty never thought it made sense for the government to engage in income splitting when it got to surplus, and clearly he was on a different page from the prime minister on that," Nash said.
"I think the prime minister will likely try to choose a new minister who represents as close to his thinking as possible."
Regardless of who gets the nod, the Conservative songbook of economic stability and those ubiquitous Economic Action Plan ads will remain front and centre, Nash said.
"My expectation is the branding will continue. They'll just have a different person out selling the brand."