have you seen the christening record for a job demaine 30 aug 1779 in thornthwaite yorks is this probably him ? , also like you I,ve looked about for an emigration record but cant find one , thing to remember is that back in the early days most folk sailed to canada then went overland to the usa a good site for early records is THE SHIPS LIST they have quite a few listings but the only demaine I could find was for a B demaine IN 1831 .
sorry i cant be more helpful .
yours
trevor