The leaders of Canada鈥檚 four national parties squared off in Toronto Thursday evening at a debate that focused mostly on the economy, environment, Senate scandal and terrorism.

In the first segment of the debate, Liberal Leader Justin Trudeau said the key question for Canadians is whether 鈥淪tephen Harper鈥檚 plan (is) working for you.鈥

Trudeau said that 鈥渨ages are shrinking鈥 and Canada needs a 鈥渇resh approach.鈥

The Liberal leader said his party is the only one committed to lowering taxes on the middle class by taxing wealthier citizens.

鈥淭he only risk right now would be to stick to what has been a failed plan for 10 years,鈥 Trudeau said.

NDP Leader Tom Mulcair also said 鈥淢r. Harper鈥檚 plan isn鈥檛 working.鈥

Mulcair said Canada lost 400,000 鈥渨ell-paid manufacturing jobs鈥 under Harper鈥檚 watch.

The NDP leader said Harper鈥檚 job creation record is 鈥渢he worst since the Second World War.鈥

Mulcair promised the NDP would invest in infrastructure, cut taxes for small businesses and champion manufacturing technologies including green energy.

Green Party Leader Elizabeth May said Canada is in a recession, and that it鈥檚 time to 鈥渂uild up Canada鈥檚 economy through investment.鈥

鈥淲e need investment from the public sector. We need to invest in a climate action plan. Frankly, we need an army of carpenters, electricians and contractors going out to plug leaky buildings,鈥 she said.

May said she was 鈥渘ot very鈥 concerned about running a deficit.

鈥淲e have a weak and shrinking economy and it鈥檚 the wrong time for austerity measures,鈥 she said.

Harper defended his record, while admitting that 鈥渨e have weakness obviously in the energy sector because of the fall in the energy prices.鈥

鈥淭he way you deal with this is by sticking with a plan that is working, a low-tax prudent plan that is working,鈥 he said, 鈥渞ather than go to a plan of high tax and high deficits that鈥檚 failing everywhere else.鈥

Harper attributed Canada鈥檚 鈥1.3 million net new jobs鈥 since the recession in part to tax cuts, and warned that 鈥渢he other guys鈥 want to impose taxes that would 鈥渒ill jobs and hurt ordinary people.鈥

Pipelines and the environment

The second segment of the debate focused on where the leaders stand on a number of oil and gas pipeline projects that have faced opposition over environmental concerns.

Harper was asked whether the Keystone XL pipeline, which would carry Alberta crude oil to Texas, would have been approved by U.S. President Barack Obama had Canada imposed a nationally set price on carbon.

鈥淎bsolutely not. The president has never said that to me,鈥 Harper said, adding that he believes Obama will 鈥渟imply make a decision that鈥檚 in America鈥檚 best interest.鈥

Harper said he is 鈥渙ptimistic in the long run about the future of that project,鈥 adding that he believes 鈥渨hoever is the next president will approve that project very soon in their mandate.鈥

Harper warned that his opponents would impose carbon taxes that will increase the cost of 鈥済asoline, home heating, groceries -- you name it.鈥

The Conservative leader accused his rivals of opposing pipeline projects 鈥渂efore we鈥檝e even had environmental assessments.鈥

May attacked both Harper and Mulcair鈥檚 positions on pipelines, taking aim squarely at Mulcair on whether he supported the Kinder Morgan project proposed for B.C.

鈥淚t鈥檚 pretty straight forward,鈥 May said. 鈥淭hey plan to put three times as many tankers moving out of Vancouver loaded with diluted bitumen, hazardous risky material.鈥

Mulcair responded that he had opposed a similar project when he was Quebec鈥檚 environment minister.

鈥淲ith regard to these other projects, we have to be able to look at them objectively through a credible environmental process,鈥 he went on.

May fired back: 鈥淪o you take no position?鈥

鈥淚 am taking the position that you can study these projects,鈥 the NDP leader said.

鈥淢s. May takes the position that you can say no to all of them in advance,鈥 Mulcair added. 鈥淢r. Harper is taking the position you can say yes to them all in advance.鈥

Trudeau took aim at both Mulcair and Harper, saying the Conservative leader 鈥渉asn鈥檛 been able to get it done on the environment鈥 and accusing the NDP leader of 鈥渋nconsistency.鈥

Trudeau pointed to the Energy East project, which would ship crude oil from Alberta and Saskatchewan to refineries in eastern Canada. The proposal is unpopular in Quebec.

鈥淚n English he鈥檒l say he supports the Energy East pipeline,鈥 Trudeau said of Mulcair. 鈥淚n French he said that it鈥檚 out of the question.鈥

Mulcair responded that Energy East 鈥渃ould be a win-win-win,鈥 offering better prices for producers, more royalties for the provinces, jobs and energy security.

Senate scandal

Harper was asked by the moderator whether he would apologize for appointing scandal-plagued senators. His answer was no.

鈥淭he Senate has been an institution that has had these kinds of problems for 150 years,鈥 Harper said.

鈥淲hen bad actions arise, the role of a leader is to take responsibility and hold people accountable and that鈥檚 exactly what we鈥檙e doing,鈥 he added.

The top Conservative reiterated his position that he will not appoint any new senators, with the goal of putting pressure on the provinces to reform or abolish the institution.

May said that Harper鈥檚 decision to stop appointing senators is 鈥渦nconstitutional.鈥 However, she said dealing with the Senate is 鈥渘ot my top priority.鈥

Trudeau said the Senate can be reformed without 鈥渄iving into constitutional reform鈥 and that any future appointments should be done in a 鈥渢ransparent, non-partisan way.鈥

Mulcair said he supports abolition 鈥減ure and simple.鈥

鈥淢r. Trudeau thinks we need better senators,鈥 the NDP leader said. 鈥淚 think we need only former senators.鈥

Response to terrorism

Trudeau said Canada should have a role in fighting the Islamic State, but he does not agree with Harper鈥檚 approach.

鈥淯nfortunately, Mr. Harper, as we鈥檝e all seen, hasn鈥檛 seen a war he hasn鈥檛 wanted to get involved in,鈥 the Liberal leader said.

Harper defended Canada鈥檚 contribution to the war in Iraq and Syria by saying NATO countries support the mission, and that ISIS has singled Canada out by name.

鈥淚t would be absolutely foolish for us not to go after this group,鈥 Harper said.

Mulcair, meanwhile, said the current mission against ISIS is 鈥渘ot a NATO mission鈥 and is a 鈥渨rong-headed approach.鈥

鈥淢s. May is opposed to every single possible use of our military, Mr. Harper is in favour of every single possible use of our military,鈥 he said. 鈥淲e will take a balanced approach.鈥

May focused on her opposition to Bill C-51, the Anti-terrorism Act passed in June that expands the powers of Canada鈥檚 spy agencies.

The Green leader said the legislation erodes the freedom of Canadians, adding 鈥渢his legislation must be repealed.鈥

Mulcair, whose party voted against the legislation, agreed.

Trudeau admitted that voting in favour of Bill C-51 was 鈥減erhaps naive鈥 and said he would repeal certain aspects of the bill.

鈥淚 think this is an issue that people are quite rightly worked up about,鈥 he added.