If you can pronounce wheelbarrow you can pronounce maori words beginning wh as maori did 50 years ago. The "F"is because some people seem to use the F word as a matter of course.
Now I get it: Wa-nga-rei.
It's simple: If you are from Whanganui, you pronounce it Wa-nga-nui. If you are from most other areas, you pronounce it Wha-nga-nui (Far-nga-nui). The pronunciation should never have been Wong-a-nui, so it would only be a cretin who'd think people might say Whong-a-nui (Fong-a-nui)!