[HKH2]

You can argue it's not as strong as a 'w' in English, but it's definitely there, enough to justify saying 'a' instead of 'an'.

[frenchyatwork]

This is kind of complicated because [u] is a rounded vowel, so it's slightly "labialized" even if it's not preceded by [w].

Additionally, English spelling rules are complete insanity, and if an English speaker sees "uhan" they'd probably pronounce the 'u' as [ju:].