The Library and Archives Canada website has a database that contains over 33,000 records for immigrants who stayed, were born, married, or were buried at the Grosse Île Quarantine Station between 1832 and 1937. The quarantine station at Grosse Île is infamous for the thousands of Irish people who died there during the Famine years. However, it has a much longer history and was first used as a quarantine station in 1832.
Grosse Île Quarantine Station was located in the St. Lawrence River and acted as a pre-immigration stopping point near Quebec. This collection of records was compiled by Parks Canada and comes from many different sources, including:
Baptisms recorded at the Grosse Île Quarantine Station
Births that occurred at sea
Burials recorded at the Grosse Île Quarantine Station
Deaths that occurred at sea
Inventory of belongings of deceased people
List of tenants of Major Denis Mahon, landlord of County Roscommon in Ireland
Marriages recorded at the Grosse Île Quarantine Station
Names recorded on the Grosse Île Quarantine Station Memorial
Some of the records in this database mention an Irish county of origin. For example, 30 year old Edward O' Reilly died on 30 May 1847 and was from County Fermanagh. He was buried two days later, on the 20th, and was married to Anne Martin.
From a random search of the records, my guess is that less than half have Irish place of origin information. The best chance of getting this information is in the records that were sourced from baptisms, burials, and for tenants from the Mahon estate. Those who are from the Mahon Estate have their townland of origin in County Roscommon listed. For more information about emigrants to Canada from the Mahon Estate, see Dr. Ciaran Reilly's guest post from last November.
You can access the database and information about it by clicking here.
 “Immigrants at Grosse Île Quarantine Station, 1832-1937”, database, Library and Archives Canada (http://www.bac-lac.gc.ca/eng/discover/immigration/immigration-records/immigrants-grosse-ile-1832-1937/Pages/search.aspx : accessed 28 April 2015), entry for Edward O'Reilly, 30 May 1847; citing Bibliothèque et Archives Nationales du Québec, Registre d'état civil, Saint-Luc de Grosse-Ile, 1834-1932, item 694.