I live in Canada…..my fiancé is in Omaha. I want to go there to visit him and get married at the same time. Can I do this?

Yes, you can. If you are a Canadian citizen, you do not need a visa to travel to the US, but you do need one to stay (if you are intending to stay).

If you are a permanent resident of Canada you likely need an ESTA or a visa before travelling.