In Abu Dhabi, a UAE source informed about the attack plot said there was "no UAE citizen" with the name Raed Jaser. The source spoke on condition of anonymity because he was not authorized to brief media.
Authorities were tipped off by members of the Muslim community, Best said.
The Canadian Council on American-Islamic Relations, a national Muslim civil liberties organization, planned to hold a news conference in Toronto on Tuesday to comment on the terror-related arrests.
A spokeswoman for the University of Sherbrooke near Montreal said Esseghaier studied there in 2008-2009. More recently, he has been doing doctoral research at the National Institute of Scientific Research, a spokeswoman at the training university confirmed.
Julie Martineau, a spokeswoman at the research institute, said Esseghaier began working at the center just outside Montreal in 2010 and was pursuing a Ph.D. in nanotechnology.
"We are, of course, very surprised," she said.
A LinkedIn page showing a man with Esseghaier's name and academic background said he helped author a number of biology research papers, including on HIV and cancer detection. The page says he was a student in Tunisia before moving to Canada in the summer of 2008.
The page carries a photo of a black flag inscribed with the Muslim declaration of faith: "There is no god but God and Muhammad is his prophet." The same flag was used by al-Qaida in Iraq and then started being used by ultraconservative Islamic groups in Egypt, Tunisia, Mali and elsewhere across the region.
In Markham, Ontario, north of Toronto, police tape cordoned off half of a duplex, with officers remaining at the scene well into the night. Sanjay Chaudhary, who lives in the other half of the duplex with his family, said the RCMP questioned him about his neighbor Jaser, asking whether he knew him or spoke to him often.