Genealogy / Family History Search: Anton Kulchinski, b. 5 Apr 1845 (E. Prussia, Germany or Poland) to America 1878. [4]

Anton Frank Kulchinski b. 5 Apr 1845 in either E Prussia, Germany or Poland. To America around 1878, He had a boat business on the Vistula, perhaps.
Wife Alvina Wiesnewski (sp?) b. 1 Mar 1851 either E Prussia, Germany or Poland. To America around 1876, she had 7 brothers.
They lived near Chelm and Torun, but have no other information other than that.
4 children born before move to America: Albert, Matilde, Melia, and a baby boy who died.
Where would be a good place to start (Am on Ancestry.com and Family Search. Have checked US records, can't find naturalization papers. Passenger lists just say "Prussia")?

I do not speak Polish.
Thank you for your ideas.