Are you certain it was Maryann and not Martha? There is a record of Robert and Martha (Antony) Brown marrying 27 Dec 1829 The transcripts from the Anglican Baptism Records could have been incorrectly transcribed. You can access the originals by contacting the church directly:
St. Paul’s Anglican Church
Cochrane St
PO Box 341
Harbour Grace, NFLD NF A0A 2M0
I am a Solomon Brown descendant, brother of Robert Brown. There were so few Brown’s in Spaniard’s Bay at that time and so it seem highly likely that Robert is the Robert you are looking for. However, I do find a death record for a Mary Ann Brown age 36 date of death 20 Feb 1842. Her records are at the Holy Redeemer Anglican Parish Office PO Box 89, Spaniard’s Bay, NF A0A 3X0.