CALGARY — The upcoming federal election is casting a cowboy-sized shadow over the Calgary Stampede as party leaders wrangle for votes.

This happens every year as the top political gunslingers take verbal shots at each other during the week-long event.

But there's a different urgency this year with a pending federal campaign following the surprise victory by the Alberta NDP in the May provincial election.

Calgary Mayor Naheed Nenshi said the Alberta NDP win over the Progressive Conservatives could be a sign the New Democrats and the Liberals are poised to challenge Stephen Harper in his home province.

"It may well be that this city is in play for the first time in my lifetime," Nenshi said Friday.

"It doesn't necessarily mean Thomas Mulcair is going to find super fertile ground here, but I think it means Calgarians and Albertans have said we can do different things.

"I think in a number of ridings in Calgary and Edmonton where you've got very strong Liberal or New Democrat candidates there may well be a breakthrough here so we'll see what happens in the fall."

Harper was asked if the Stampede marks the beginning of the barbecue circuit for the Conservatives as the party prepares for a federal election.

"It always is. I have my own barbecue tomorrow night. That is always kind of the first of the summertime barbecues that we have around the country. So in that sense this year is no different than any other," Harper told CTV Calgary.

Mulcair, who watched the parade with his family, said his party has been on a roll dating back to the 2011 federal election.

"People have been looking at us very closely as a matter of fact and the breakthrough here in Alberta followed a breakthrough in Quebec in the 2011 campaign. It really shows that the NDP does represent change," he said.

Liberal Leader Justin Trudeau said the new reality in Alberta is that change is possible.

"Long-time Liberals in Alberta have become used to a certain level of unpopularity because of their Liberal-ness. No one becomes a Liberal in Alberta because it helps them get into a country club or better social circles or contacts," he said. "I think people are realizing there are options."

Premier Rachel Notley, who is to meet with Harper on Monday, isn't surprised the three main party leaders are wooing voters in Calgary.

She said the traditional Alberta electorate is getting younger and more progressive and the success of her party in May is having a cascade effect.

"I think it shows that those people who want to vote for the leadership of Tom Mulcair and the leadership of Canada's NDP, they feel that that vote is one that can win," Notley said.

"I think that's what our win here taught them — that it's not necessary for them to vote for their second choice for the sake of strategic voting. They can vote who they want to. So I think that's what's helping Tom Mulcair's NDP and we'll see what happens with it."