Unfortunately, your gt.grandfather died at a very inconvenient time as far as Quebec death records are concerned. Records of deaths between 1900 and 1926
are available only from the following office:
Ministère de la Justice
Direction de l’état civil
Service à la clientèle
205, rue Montmagny
Québec, QC
Canada
G1N 4T2
If you write to them in English, I am sure they would answer. I think the cost is about the same as UK certs. Give full details of your gt. grandfather, date and place of death (city or town where his ship was docked when he died). And most important, be sure to include his religion. Religion would be very important as death records in Quebec were kept by churches ( a duplicate of church registers deposited at the court house, served as civil registration). There was no real civil registration before 1994.
If there is any truth in the murder story or even if he drowned, there would have been an inquest and perhaps newspaper reports. These are other avenues
that you might explore.
If you would like some more help, I am willing to do some online searching, if you can give me his name and the place where he died. I don't know if there is much to be found online, but as I have done genealogical research in Quebec, I might be able to find something.
hth,
Carmela