But regardless of the allegations against the assassination victim, India would have no right to kill someone on Canadian soil, no matter the justifications it might have.
Extraterritorial killings are not justifiable, and definitely not by events that occurred 38y ago.
Hopefully this is all false and India wasn't involved in the murder of this person. But if true, it's inexcusable and paints India in a very bad light in term of international reputation.