There wouldn't be a lot of information for you, only perhaps parish records with baptism and marriages. Too early for the Griffith Valuation now used as a census substitute but
the Tithe Applotments fit the years mentioned above 1823-1837:
Even families living in the same areas from 200 years ago often don't know they had family who emigrated and are surprised but always hospitable when you turn up on the doorstep.
If you want to know more about living and social conditions there books. In in particular written by an American woman visiting Ireland in the 1840's.
www.from-ireland.netThis was the time of the Great Famine whose worst years were from 1845-54 but there were previous famines as well. During the Great Famine Ireland was producing enough cattle, sheep and grain enough for export to the UK but not for the people of Ireland.
Tithe Applotments:
www.genealogy.nationalarchives.ie51 Early's
12 Thomas Dillon's
Robert Dillon, Parish Creagh, Townland Culliagharny sharing land 35 acres.3 roots.8 perches
Patt Dillon
John Dillon
Robert Dillon, Parish Killinvoy, Townland Gurtagne 50.0.0
No way to tell if either of the two Roberts are yours, or the father, grandfather etc. Usually due to the British land reforms only the lst. son could transfer land and so younger brothers would need to get their own land or emigrate.
Baptism and marriage records for Roscommon are on line with
www.rootsireland.ie (undergoing maintenance at this time)Both names are not common unlike John
Depending on the survival of parish records you should be able to find birth records for 1800.
Many passengers would come to Canada first as the passage was cheaper and then move into the USA, or settle and later move. Perhaps to pursue better land.
www.theshipslist.comwww.igp-web.com can be a good website depending on the county
www.familysearch.org has some early Roscommon records for just a few parishes but this is rare. Civil Registrations from 1864 for birth, marriages and deaths.
www.census.nationalarchives.ie (newly added extracts that survived from early census)
used to only be 1901/1911 until recently.
Annette Code