The Haftarah of Bamidbar is the second chapter of Hoshea. It is not for the faint of heart, and has embarrassed thousands of poor Bar Mitzvah boys, including my son, Yair Eitan.
The connection is clear, and is handled by the Midrashim directly. All we have to do is understand what the Midrashim are telling us.
This doesn’t have anything to do with the Haftarah, but you might be interested in the aforementioned Bar Mitzvah boy’s Drasha on Bamidbar in which he tries to explain the rounding method used in the Torah for the population figures. Here is the text in English