Lewis could be a surname. So there is perhaps a Lewis on the maternal side of the family.
Or as other people suggested a respected friend. Who were the Godparents/Sponsors at
baptism? Have you the full name or is there a second given name?
That might give you a clue.
> My ancestor named his first born son, Lewis, born in 1826 in Ontario. The family came
here from Fermanagh in 1817. The name Lewis seems to have come out of no where; it does
not appear in subsequent Fallis families, nor have I seen the name Lewis in Fermanagh
records in that time period.
> The paternal grandfather of this child was named John; I do not have the maternal
grandmother's last name or parentage, but understand that she came from Fermanagh.
Lewis does not occur in the families of Lewis's aunts and uncles, so I am assuming it
was not the name of the maternal grandfather.
> They were Methodists.