He appears in the 1869 New York City directory: Flandreau Elijah P., cooper, 322 Wash'n, h B'kh (Brooklyn Heights?) His business also appears as: Flandreau & Bennett, coopers, 322 Wash'n
He's also in the 1889-90 Brooklyn, NY directory: Elijah P. Flandreau, cooper, West N. Y., 272 S. 5th, Brooklyn, NY
In the 1840 census in New York an Elijah Flandro (born between 1801 and 1810) shows up as head of a family of seven (male and female between 30 and 39, 1 male 15-19, 2 females 10-14, one male 5-9, and one male under 5), one of whom was employed in manufacture or trades.
I'm afraid I don't have anything else to tie Elijah to specific earlier Flandreaus.At least not yet.