"This has the potential to be a very important part of our efforts to fight climate change in Canada," Harper told supporters.
However, when it comes to federal funding for the project, Harper remained vague.
"In terms of specifics those things still have to be discussed," he said.
The governments of Newfoundland and Labrador, and Nova Scotia have been seeking financing for the project. But Quebec has argued that Ottawa contributing federal money would represent an unfair subsidy.
The talks have revolved around a federal loan guarantee to minimize borrowing costs, including for a subsea cable that would route power from the hydro project through Nova Scotia.
Harper's comments irked Duceppe, who cried foul on the idea of federal money going to the project.
"The Conservatives intend to finance a competitor of Hydro-Quebec with our own tax money," Duceppe said in Louiseville, Que.
"We never got a cent from Ottawa to finance our electrical transport lines," he added. "It's a slap in the face to Quebec."
Harper then traveled to Newfoundland and Labrador, while Ignatieff went to a Winnipeg preschool and Layton was in Montreal.
Harper is attempting to rebuild bridges with Newfoundland — bridges that had their foundations shaken in 2008 when then-premier Danny Williams took a hard position against the Tories.
The Conservatives were entirely shut out of the province in the 2008 election after Williams carried out a successful "Anything But Conservative" campaign, saying Harper had not helped Newfoundland.
This time, the party has a high profile candidate in Labrador, where former Innu Nation leader Peter Penashue has announced he will run.
In addition, Williams' successor Premier Kathy Dunderdale seems to be turning the page on the frosty relations Newfoundland formerly had with Ottawa. Several of her cabinet ministers have been seen at Conservative candidate nomination meetings in recent weeks, The Canadian Press reports.
Harper also said he would turn Halifax Harbour into a hub of international trade with India and the European Union, if his party is re-elected to government.
Speaking at a shipping yard, the Conservative leader said his government would move ahead "full throttle" to complete historic free trade agreements already in progress.
"We are aiming and we are on track to achieve agreement with Europe early next year, 2012, and India the year after that, 2013," Harper said.
He then quickly launched into a grim warning about the Liberal track record on free trade pacts, and how a coalition involving the Liberals, Bloc and NDP would damage Canada's international trade relations.
"Imagine today's Liberal Party locked in a parliamentary alliance with the Bloc Quebecois and NDP, trying to negotiate trade agreements. The one hardly ever votes for trade deals, the other never does," Harper said.
"Michael Ignatieff would face more haggling in his own government than he would with foreign trade negotiators. It would be a gong show."
In the scrum after the announcement, Harper faced questions about whether he would agree to a one-on-one debate with Ignatieff in addition to the party leaders debate.
While Harper had suggested he was open to the idea, and Ignatieff said he was ready to take part, the Conservative leader said he was only interested in one debate, and that would be the debate that included the NDP, Liberal and Bloc leaders.
Harper was also grilled on why he was limiting questions from reporters at his news conferences to just four.
Harper didn't give a direct answer, instead saying if there were issues he hadn't addressed, he would take more questions. He then proceeded to take two or three other questions before ending the scrum.
Meanwhile, New Democrat Leader Jack Layton visited Montreal to help shore up support for Thomas Mulcair, his deputy leader and the NDP's sole MP in Quebec.
Layton believes he can gain ground in the province, which is also expected to be a prime target for the Conservatives and Liberals.
The NDP leader is expected to focus on environmental issues in Quebec. During his speech, he pledged to scrap $2 billion in government subsidies for the oilsands and put the money toward more green-friendly energy projects.
One day earlier, Layton laid out a $2.3-billion jobs plan that would lower small business taxes and offer a tax break for hiring new employees.