Foreign Affairs Minister John Baird's office is calling suggestions for an emergency debate in the House of Commons "premature" as Canada reviews a "full range of options" with international partners.
British Prime Minister David Cameron has recalled the U.K. parliament for Thursday. The U.S. defence secretary said American military forces were ready to attack if ordered, but no course of action has been determined yet by that administration.
Harper and U.S. President Barack Obama spoke by telephone in the morning, with the two leaders finding consensus that the Syrian regime used chemical weapons against its own people last week.
UN inspectors are still in the midst of an investigation, but the U.S. has said it has its own intelligence pointing to the regime of Bashar Assad.
"Both leaders agreed that significant use of chemical weapons merits a firm response from the international community in an effective and timely manner," said Andrew MacDougall, a spokesman for Harper.
Baird called opposition leaders throughout the afternoon to discuss the unfolding crisis.
"We have been in close contact with our international partners and will continue to work with them in lock-step," said Rick Roth, a spokesman for Baird.
"Canada believes the only way to halt the bloodshed in Syria is though a political solution, however, we understand that this solution is becoming more and more difficult as the crisis enters a dangerous new phase."
Roth added that "the complete obfuscation of Russia at the (UN) Security Council needs to end, and they need to now become part of the solution."
Mulcair's spokesman George Smith said the NDP leader "was very clear with Minister Baird that Parliament would have to be recalled if there was any direct military involvement. Mr. Mulcair also stressed the importance of working with the United Nations."
Liberal Leader Justin Trudeau, in P.E.I. for a Liberal caucus retreat, said Canada needs to proceed prudently before undertaking any military role in Syria.
"As soon as we talk about military intervention, there are many, many questions unanswered. Like what would military victory look like? Who would we be helping?" Trudeau said.
"There are grave questions, both about the government side but also about the rebel side. That's where we have to have honest and open dialogue about it. And I'm certainly not going to pretend that anyone has all the answers."
The Arab League flatly blamed the Syrian government for the attack that activists say killed hundreds of people last week. The league said the perpetrators must be brought to justice.
Syrian Foreign Minister Walid al-Moallem denied his government was behind the attack and challenged Washington to present proof of its accusations.