Looking for records on Kehoe ancestors

I'm at a dead end with my Kehoe ancestors.  My Ancestry DNA profile shows all of my mother's family from Munster, Beara Peninsula.  I have had no luck finding any information on any of them prior to them leaving in the early 1800s.  The earliest Kehoe I can find in my cousins' family trees is Michael Kehoe.  They say he was born in Cork in 1791 and died in New Brunswick on Aug 6, 1859.  I cannot find any documentation of any Kehoes in that area at all and cannot find any documents for the O'Shea and O'Sullivan families either.  I know my second great grandfather Jeremiah "Darby" O'shea was born in Cork in 1803 and my second great grandmother Catherine O'Sullivan was born there in 1810.  But that's all I know.  I've tried every Kehoe spelling I know of but still find nothing.  Were they born too early to find records online?  I know the O'Shea and O'Sullivan families arrived in New Brunswick in 1826.  Looking for anything (like passenger manifests) to give me more info on point of origin. Canadian records have been no help, listing birthplace only as Ireland.  Anyone have suggestions?