Did he ever live in a place called Quamba in Kanabec county in Minnesota? A man named John Oberg with a wife Hilda lived there on 12 September 1918. His birthdate was 5 March 1886, according to the World War I Draft Registrations on the Ancestry.com site. He was a produce merchant, had blue eyes and brown hair, etc.
I suppose his last name was spelled Åberg or perhaps Öberg in Sweden, but there is little to distinguish your John (perhaps Johan or Johannes or Jan or Jon or Jöns etc. in Sweden, and he may well have used other given names in addition to John). When did yours emigrate? There is a column for a year of immigration on the U.S. Federal Censuses for 1900-1910-1920-1930. Check all of those censuses. I know you said 1903 but maybe it was a year or so earlier or later than that.
He most likely was naturalized after the time period (late 1906) when the naturalization forms were standardized across the country. If so, his birthplace, birthdate, port of departure, name of ship, port of entry, date of entry, etc. would be listed. If he had been married to Hilda when he naturalized, the same sort of information was probably listed for her.
The NARA (National Archives and Records Administration) regional archive in Chicago has at least some naturalization records for Minnesota, but they are not online.
http://www.archives.gov/great-lakes/chicago/finding-aids/naturalization-records.html Ship manifests became much more helpful in that time period, so obtain his (perhaps online but often just on microfilm) to see if he had good information on his.
Many of our Swedes emigrated with a patronymic (son/dotter) name and only later changed to a surname. Here is a maybe for John from the Emibas CD, made from registrations in the Swedish parish before going to a foreign country. Emibas is only about 75% complete, and probably even less complete for records as late as 1903.
Post 159544
Johansson, Johan Henning
Dräng (unmarried man)
b. 3/5/1886 in Fröderyd, Jönköpings län (Småland)
Emigrated 3/11/1903
from Flathult, Fröderyd, Jönköpings län (Småland)
to Nordamerika
Source: Household Examination Roll, p. 52
Emibas migration file ID: Fröderyd F 1903 014
(Dräng = farmhand.)
There is not enough information yet to definitively say if that man is yours or not.
If you have ordered his Social Security application, you would know his birthdate, perhaps his birthplace and probably his parents, including his mother's maiden name. I don't see him on the Social Security Death Index (which mostly has names from the mid to late 1960s and later) but if you can find his Social Security number on a death certificate, you can order the application. (It costs $27.)
It may be best to use the Swenson Swedish Immigration Research Center. They have fantastic records but those records are not online.
http://www.augustana.edu/swenson/ Judy