Migration Routes, Waterford - US, 1840s?

From what port would persons living in or around Dungarvin and Abbeyside have likely left to travel to America in the mid to late 1840s? Would they have gone to Cobh/Queenstown, or across the water to Liverpool ? Or did transAtlantic shipping directly serve the Waterford ports?

I'm trying to track down William Douglas, whom I believe to have been born on the Isle of Man ca.1820. He married Anne Grant of Abbeyside in either 1843 or 1845, and had a son named William in 1845 in Waterford. The next trace I can find so far is his Declaration of Intent to Naturalize in New Orleans in Sept of 1849. I'm almost certain that I've found him as a night watchman in Louisiana in the US 1850 census.

The records may not have survived. There are many gaps in early -to-mid nineteenth century US passenger lists. I'm also told that many ships went from Ireland to Canada, with people traveling south to the US from there.

Any suggestions will be appreciated. Many Thanks!