How to find Mariner's Names circa 1840?

[LUV]

Searching on a small lead...that a daughter of my Great Great Great Grandfather met the ships "captain" on their way to Canada from England in 1845.  This daughter and this "captain" married either aboard or in Halifax Canada and she returned with him to England?  Her last name was JARVIS.

Rather romantic if nothing else!

I cannot find the ship they would have come over on.  Passenger lists for this time period are sporadic.  How can I follow this lead?

His last name was Saunders?  And I am not sure if he was a "Captain" or not...what actual job he would have held on the ship.

Any and all help appreciated!