The Mary Ann Luke might be the 1818 daughter of William Luke and Mary Trembeth. She is about the right age to have a son about 1837, and her parents did come to Oshawa, where her father died in 1842 and her brother Thomas in 1845. Thomas had been married at Whitby Township in 1835.
I say "might be" because I have yet to trace her. So she is only in my St. Blazey Families tree at http://trees.ancestry.com/tree/20919668/person/1146274970
and not yet in my Columbus Families tree. But she is the only Mary Ann Luke of the three I have found who seems to fit on all aspects.
She was born at Parr (spelled thus and not the current standard Par), which was then part of St. Blazey parish but has since become a separate parish. She was baptized 5 Oct 1818 at St. Blazey.
There was another Mary Ann Luke (abt 1795) at St. Blazey who probably has connections to East Whitby, through her 1817 St. Blazey marriage with William Mark, but this too has yet to be followed through and verified.
And the third Mary Ann Luke (bap 1 Oct 1821 at St. Blazey) died 4 Apr 1845 unwed and is buried in the Oshawa Pioneer Memorial Garden.