Bolland Family from Trondheim

Seeking information about the emigration of Mikkel and Mary (also called Marit) Bolland. They appear in the US Census for 1880 in Hesper, Iowa aged 50 and 55 respectively and would probably have left Trondheim in the 1850's - or earlier. 1st child born in Iowa in 1860 so it would be before that time. I'd like to trace the ship but am unsure whether they landed in the US or in Canada.