"We all know majority governments don't typically fare well in byelections, the opposition parties do," said Cory Hann, communications director of the Conservative Party.
"And these rounds we don't expect to be any different."
The Conservatives anticipate hanging on to the two Alberta ridings but do not expect to win more than 10 per cent of the vote in each of two Toronto-area contests, said one senior Tory insider, who spoke on condition they not be named.
"The two Ontario ridings, I think the writing's on the wall on those," said the source, who picked Justin Trudeau's Liberals to win both fights.
"If there's a race, the two horses in that race are going to be the NDP and Liberals."
Prime Minister Stephen Harper announced Sunday that voters in the four ridings would go to the polls Mon., June 30, in the middle of what for many will be the four-day Canada Day weekend.
The timing, and unusually long seven-week campaign period, were intended to steer completely clear of the June 12 Ontario election, the Conservative insider said.
The byelections will provide a glimpse of the fevered political jostling well underway in the runup to a general ballot next year.
The Alberta constituency of Fort McMurray-Athabasca was vacated by Conservative MP Brian Jean, who stepped down in January, citing a desire to spend more time with his family.
Conservative MP Ted Menzies resigned his southern Alberta seat in the riding of Macleod in November to become president and chief executive officer of CropLife Canada, a trade association for plant-life technologies.
"We'll likely hang on to those," the Conservative source said. "That said, we're obviously not going to take them for granted. It being a byelection, it's always a different beast."
Trudeau is working to prove the Tories wrong, campaigning in Fort McMurray-Athabasca during the weekend with candidate Kyle Harrietha and tweeting that there's an "appetite for change" in the region, a hub for oilsands development.
Canadians are looking for representatives who will bring their local interests and concerns to Ottawa, Trudeau said Sunday in a statement. "Under Mr. Harper, all they get in return is the voice of the prime minister in their community."
NDP national director Anne McGrath touted party leader Tom Mulcair's "balanced approach" to resource development in Alberta at a time when Canadians are taking a hard look at the environmental and economic implications of the oilsands.
"There are a lot of people who are looking at Stephen Harper's Conservatives and not very happy with what they see, and they're looking for an alternative," she said.
In Ontario, the byelections will unfold against the backdrop of the hotly contested provincial election and a high-profile mayoralty race featuring troubled incumbent Rob Ford, who has forged close ties to senior federal Conservatives.
Toronto's Trinity-Spadina became vacant when New Democrat Olivia Chow — widow of former party leader Jack Layton — resigned to challenge Ford for the mayor's job.
Stephen Lewis, an NDP luminary and former Canadian ambassador to the United Nations, endorsed party candidate Joe Cressy, who is fighting Liberal nominee Adam Vaughan, a city councillor, for the riding.
"Joe Cressy is a rare breed in politics: intelligent, compassionate, tough, principled," Lewis said Sunday.
In suburban Scarborough-Agincourt, Liberal stalwart Jim Karygiannis stepped down to run for a seat on Toronto city council in a ward that overlaps much of the federal riding. It's turf the Liberals have held for a quarter century, making it Grit candidate Arnold Chan's to lose.
Harper did not call a byelection for the Ontario riding of Whitby-Oshawa, left without an MP upon the recent death of Conservative Jim Flaherty, the former finance minister.
The riding was not part of the mix this time out of respect for both the family and the parties, since none has yet nominated a candidate, the senior Conservative said.
Follow @JimBronskill on Twitter
Also on HuffPost