McMahon Family Found... Maybe!

I think I have just made a major breakthrough on my McMahon family. The family has lead me many directions but this looks really good.
My great great grandfather Cornelius McMahon was born somewhere in Co. Clare in 1823. He married Sarah McCue and settled in Ayton, Normanby, Twp., Grey Co., Ontario, Canada. We know he had 3 brothers at least, Michael, Edward and John. His first son Michael died at the age of 18 and is buried in in the Orchardville Cemetery in Normanby. When I asked someone to take a photo of his stone quite a number of years ago I was surprised that it also had another Michael mentioned on the headstone. It reads Michael d 28 Jan 1856 age 50 yrs.
I did all I could to try and locate some sort of death record, to no avail. I assumed that Michael sr. was the father of Cornelius and his brothers.
The next puzzle was the 1861 census which had a John and Maryann McMahon living with Cornelius, they had later birth dates then his children so I assumed cousins. The interesting thing was that they listed Sherbrooke, Quebec as their birthplace.
I had found this record on Automated Genealogy before, which has a family that could possibly be mine  but after contacting the local archives for the children John & Mary Ann's birth and nothing was found, I had set this aside.
Well I was prompted by a relative in Michigan to have another look a couple of days ago and thanks to some wonderful help and ancestry.ca, this record was obtained

Which translated for me by someone who can - 

The 15 February 1852 we did bury in the cemetery of this town the body of Mathilda, died the night before at the age of 8, legitimate child of Michael McMahon and Margaret McNamara of this parish. Present were Michael Dolan (?) and Charles Chamberlain, who have not signed

The McNamara name is not new - as one of the brothers, Edward McMahon, died in 1920 in Lockport, New York, and on his death record his parents were listed as John McMahon and Margaret McNamara. 
Next step is to see if I can find a death record for Margaret McMahon, so back to ancestry.ca and I found this - 

Translated by a kind person-
The 31 October 1851 we buried in the Cemetery of l"Hopital de la Marine the body of Margaret McMahon who died before yesterday at the said hospital at the age of 46, came from Ireland on board the vessel (sorry I can't make out the vessel name) Present were Thomas Buckley and Louis Naulin, who did not sign.
Possible ship name - Sylvanus. i haven't been able to locate this ship coming to Quebec that year. I may have to try the Quebec newspapers and see what can be found.

The hunt is on!
There are other McNamara's that settled in Ayton, Ontario. Particularly a Daniel McNamara who married a Mary McMahon! I have sent out some e-mails and am waiting to hear back. I have so much to explore, I wonder if they would do a DNA test? The Family Finder at Family Tree DNA might help us along, but there are a lot of paper trails to follow!

It's not solid yet, but the best leads I have found in a long time and it is looking good so far!

Sorry the housework is just going to have to wait!