I have the feeling that the word one is not always pronounced in all accents (but I cannot say which exactly) with the same vowel that cup or love. I believe that with accents where we pronounce cup [kɐp], we pronounce one [wɐn], but with accents where we prounouce cup differently, we often pronounce one [wɐn] or even [wän]. Is that a right feeling ?
In accents in the north of England, where there happens to be no foot-strut split, a majority of speakers use /ʊ/, realised as [ö], in words like love and cup. This is the same vowel that RP speakers use for the word soot.
I have no idea if this is related in any way, but in many accents in the north of England there is a preference for the vowel /ɒ/, realised as [ɒ], for the word one, giving us the pronunciation [wɒn]. This word then rhymes with words such as don or gone. In contrast for a majority of RP speakers, this word, as noted by the Original Poster, rhymes with sun and would be transcribed as /wʌn/, [wɐn],
Notice that I said for the "majority of RP speakers" in the paragraph above. The renowned Longman Pronunciation Dictionary gives /wɒn/ as a variant of one and a minority of RP speakers do also use it (including me).