Voyage to America 1861

I'm trying to locate passengers Knud Sjursen and Agothe Ingebrigtsdatter and their young sons, Gabriel Elias Gabrielsen and Engel Saeverin Knudsen. A distant relative told me they "left for America on 15 April 1861 but there is no record of the children arriving in America." (We believe the boys died at sea.) Unfortunately, the relative who gave the date has refused to provide the name of the ship or ports of departure/arrival, so I'm not sure whether his information can be trusted. In 1860, I believe the family was living in Sveio, Hordaland. I've found a ship called the Maple Leaf that departed Porsgrunn on April 15, 1861, but I'm not sure why they would have been on this boat since both Stavanger and Bergen are so much closer to their home. Also, I don't know whether they sailed to Canada or America as their first known residence in the USA was Wisconsin. Thanks, Sara