with plotting to set off the three home-made devices outside the parliament building in Victoria, the capital of the Pacific Coast province, during Canada Day festivities on Monday.
Police said the two suspects "were inspired by al Qaeda ideology." But there was no evidence to suggest a foreign link to their planned attack.
The suspects were identified as John Stuart Nuttall and Amanda Korody, Canadian-born citizens from Surrey, British Columbia, about 30 km (19 miles) southwest of Vancouver. They were arrested on Monday in Abbotsford, near the US border.
Officials said they had monitored the pair since February and that the public was not at risk, since agents had made sure the bombs would never have exploded.
"This self-radicalized behavior was intended to create maximum impact on a national holiday," Wayne Rideout, assistant commissioner of the Royal Canadian Mounted Police, told a news conference. "They took steps to educate themselves and produced explosive devices designed to cause injury and death."
Canada's spy agency has expressed concern that angry and disgruntled Canadians could attack targets at home and abroad.
It says some are self-radicalized, and have learned about al Qaeda from the Internet or reached out to the group's operatives.
"Yesterday's arrests demonstrate that terrorism continues to be a real threat to Canada," federal Public Safety Minister Vic Toews told reporters in Winnipeg, Manitoba.
Police declined to detail any connections between the two and the al Qaeda network and said they were not aware of any ties to the April 15 bombings at the Boston Marathon, where three people were killed. The Boston bombs were also built from pressure cookers.
Instructions on how to make pressure-cooker bombs have been published online in al Qaeda/Yemen's English-language Inspire Magazine, and US investigators believe the Boston bombers drew on those instructions to build their devices.
'Will not let them win'
British Columbia Premier Christy Clark said the news was profoundly shocking.
"We will not let them win. We will not let them strike fear into our hearts. These public spaces belong to us, and we're going to keep them," she told reporters in Victoria.
Police said they seized the devices outside the legislature on Monday, but gave no further details.
"As these devices were constructed, we were in very tight control and we were confident public risk was absolutely minimized," said Rideout.
Canada Day is the equivalent of the Fourth of July Independence Day celebrations in the United States, with street parties, barbecues and fireworks displays, including a big celebration at the British Columbia parliament building.
Victoria is at the south end of Vancouver Island, 100 km (62 miles) southwest of Vancouver, the province's biggest city, which is on the mainland.
In April, Canadian police arrested two men and charged them with plotting to derail a Toronto-area passenger train in an operation they say was backed by al Qaeda elements in Iran.
Police also say Canadians took part in an attack by militants on a gas plant in Algeria in January.
Canadian resident Ahmed Ressam, an Algerian citizen, tried to cross into the United States from British Columbia on a mission to blow up Los Angeles airport in 2000 and is serving 37 years in a US prison.