Should Canada investigate whether Canadians are actually involved in committing or inciting terror or should we simply take India's word for it? From what has been published, Nijjar's work in Canada has been solely political; any evidence Nijjar was working with them would have resulted in him never getting citizenship.India has been asking for Canada's cooperation for YEARS. So far the response has been what you'd expect from someone being asked to investigate his own crime. See? Two can play that game.
Yes there are Sikh terrorists as designated by Canada but I would expect Canada does a decent job of researching citizenship applicants.
Canadian citizens are Canadian citizens and evidence a foreign government is involved in their killing needs to be investigated. Would you be okay if Canada shipped you back to India simply because they accused you of terrorism?