Commendable of Trudeau to actually raise the issue--though also, one would think Canada might take a bit more exception to a foreign government killing a Canadian citizen in Canada. Simply complaining about it and expelling a diplomat doesn't seem sufficient.
The West has unfortunately a track record of being very soft on foreign death squads. We did the same thing when Russian and Iranian death squads killed people in Europe:
Canada realistically can’t do anything. A more realist government might say similar things in public and then mysteriously a high ranking Indian official involved in the killing would fall out a window.
A better realist would use the opportunity to review extradition arrangements and start an official intelligence sharing organization which the Indian government would pay a substantial amount to be a part of.
Bring them out of the Stone Age, don’t get in the mud with the pig. You both get dirty and the pig likes it.
A fair question. Sanctioning individuals would theoretically be possible. Someone who knows more about this can chime in as to the pros and cons (unlikely such a person lurks on HN), but I think there may be what might be termed an asymmetry here where many (maybe most?) of the responses that would make the Indian government feel punished would be things that would hurt Canada as well (e.g. sanctions).
As the other poster said, Canada could also do some tit-for-tat shady shit. Maybe Trudeau's dad would have been willing to do that, who knows.
I heard they hit people associated with this separatist movement in four countries within a few days, Sayaret Matkat style.