Chatting by phone on the escalating crisis, Harper "made it clear that he shares the view that the recent chemical weapons attack was carried out by the Syrian regime and described the use of these weapons as an outrage," a statement from the Prime Minister's Office said.
Both leaders concurred that the government of Syrian President Bashar al-Assad has appeared to try to "obscure evidence" of the attack, the statement said.
The phone call came as Canada's top general was in the Middle East meeting military chiefs from the U.S., Europe and several regional countries to discuss those possible responses, according to reports.
The two-day summit of military brass in Amman also included the chiefs of defence staff from Britain, the United States, Turkey, France, Germany, Italy, Saudi Arabia, Qatar and Jordan, an official source in Jordan's armed forces told the country's semi-official Petra news agency.
The Canadian government would not confirm that General Tom Lawson is attending the meetings. But various reports say the defence chiefs were discussing the threat to regional security posed by the ongoing civil strife in Syria, and in particular impacts on neighbouring Jordan, where 500,000 Syrian refugees have spilled over the border.
Jordan, a Western ally, would be particularly vulnerable if the Syrian army is in fact now using chemical weapons to suppress the 2½-year-old rebellion, as the U.S., Canada, Britain and Arab League affirmed this week.
Jordanian Foreign Minister Nasser Judeh said the talks are looking at "scenarios on the ground, especially after the recent dangerous developments," according to the Agence France-Presse news agency.
AFP said Jordan expressed refusal to be used as a "launch pad" for possible military strikes on the regime of Syrian President Bashar al-Assad, consistent with Amman's long-stated preference for a diplomatic solution to the civil war, which has claimed 100,000 lives.
However, a report last week in France's Le Figaro newspaper said Jordan helped the U.S. train hundreds of Syrian rebel commando fighters on its territory.
Canada has so far resisted any military assistance to the Syrian rebels or the prospect of partaking in armed strikes, preferring to offer humanitarian help.
Andrew MacDougall, the prime minister's communications director, repeated Tuesday that it is "premature to discuss roles" that Canada could play in an eventual military operation.
Opposition Leader Tom Mulcair said Monday he wants Parliament recalled before Canada commits to any armed intervention. He added that any military offensive against the Assad regime should be debated at the United Nations first.
"To see a government in the 21st century gassing its own citizens is an abomination and the world has to move against that, Mulcair said. "That should be done through the institutions of international law, in particularly the United Nations."