Immigration before 1850

My gg - grandfather supposedly immigrated from Norway to Wisconsin before 1850 (possibly 1845-50). His fist name was Peter and U.S. "records" show a last name of Ondell, Ondall, Ollendorf and Undell. I do not know what last name he used when he arrived in Milwaukee - perhaps it was either a farm name or his fathers (son) name. Most records show he was born 1814 or 1817. Unfortunately, I only have a few guesses regarding his family farm or parent's names.(One is that he was Peder Petersen (b. 1817 in Uldalen, Oppland), but have no proof or links. Question #1 - Where can I go to get a list of pre-1850 immigrants to Wisconsin or possibly Canada? There are probably not nearly as many immigrants as 10 to 20 years later. A county history book (La Crosse, Wisconsin - 1870) "reported" that he came to Milwaukee, Wisconsin and then to Walworth, Whitewater county (abt 1850) before moving to Monroe county(abt 1859) and finally La Crosse county (1880). The same county history book "reported" that he had two sons that were born in Milwaukee - Charles (b, 7/28/1851) and Louis/Lewis (b. 12/15/1852). The 1850 census places him as working in Walworth county that is adjacent to Milwaukee county and in 1850, conditions there were quite primitive and undeveloped, so his wife may have stayed in Milwukee. Later children were born in Whitewater, Walworth county in 1854/55 and 1857. Question #2 - Where can I go to in Milwukee (only 300 miles away) to find records this old with "reported" birth dates? - Most Milwaukee records start about 1854. Any and all advise will be appreciated. Dick