The Haftarah of Naso is the story of the birth of Shimshon, from the book of Judges.
Usually, we say that the reason this Haftarah was chosen for Parshat Naso is that Shimshon was a Nazir, and the laws of Nazir appear in Naso. This is undeniable; however, there is also a connection to the related topic of Sotah:
As to why and how Nazir and Sotah are linked, that is for a different time. Likewise for the use of the word “פלא” in the laws of Nazir and in the Haftarah.