In my efforts to track down my eloped 3xgreat-grandparents Edward McDowell and Susan of unknown surname (he'd been her family's coachman, possibly somewhere near Plymouth in Devonshire, and she was 'cut off with an angry shilling' according to folklore after she ran away with him), I'm using their children's birthplaces as some kind of guide to their early life together, during which time Edward was in the navy, serving aboard the Royal Sovereign. One son, John, was baptised in Dublin. Another, Edward (jnr), later claimed (1861 England census)to have been born in 'Trabash'. Some survey official wrote 'Ireland?' beside this answer. However, in 1871 and 1881 censuses, Edward (jnr) claimed to have been born in Quebec, so perhaps Trabash is a corruption of 'Trois'-something in that Canadian province. I would be very grateful is someone who knows Quebec well has a few ideas. Perhaps the name was the location of a naval barracks or was on or, at least, near the coast.
I don't know if this will help or make things worse. The vital and church records of Quebec (Collection Drouin) shows one Edward McDowell, baptized September 27, 1820, born August 22nd on a ship from Quebec City going up to Montreal. The parents names do not match the ones you gave however, the document is hard to read but the father appears to be one Myles McDowell and the mother one Bridget White. The record says they were from Galway, Ireland. They had been living in Montreal for a month. Myles McDowell was apparently a tailor.