In addition to the Canadians, the Algerian prime minister said the militant cell included men from Egypt, Mali, Niger, Mauritania and Tunisia, as well as three Algerians.
Officials in Canada could not immediately confirm whether two of the attackers were citizens.
"Canada condemns in the strongest possible terms this deplorable and cowardly act and all terrorist groups which seek to create and perpetuate insecurity," said Chrystiane Roy, a spokeswoman for the Department of Foreign Affairs.
"We are pursuing all appropriate channels to seek further information and are in close contact with Algerian authorities," she said in a statement.
The Algerian prime minister indicated that this operation was not -- as the Islamists had claimed -- an immediate reaction to France's recent military intervention against Islamists in neighboring Mali, since the captured militants said it took two months of planning. But he said the group did come from northern Mali, hundreds of miles away from the gas plant.
He said the group included a former driver at the complex from Niger and that the attackers "knew the facility's layout by heart."
They wore military uniforms, state TV reported, bolstering accounts by escaped hostages that they didn't just shoot their way in.
"Four attackers stepped out of a car that had flashing lights on top of it," one of the former hostages, Liviu Floria, a 45-year-old mechanic from Romania, told
The Associated Press
The prime minister said "the last words of the terrorist chief" was to slaughter the hostages.
"He gave the order for all the foreigners to be killed, so there was a mass execution, many hostages were killed by a bullet to the head," he said.
Three Americans died in the attack and seven made it out safely, a U.S. official in Washington said, speaking on condition of anonymity because he was not authorized to speak publicly. Their bodies have been recovered, the official said.