If I understand correctly, Cantonese sounds very different from Mandarin, despite being written in the same way (omitting some small differences, which are irrelevant for the question).
If it is the case, how can foreign words be transliterated into Chinese on a phonetic basis, so that both Cantonese and Mandarin would read them similarly?
For example, suppose there is a Western company "Blablawabla" and I am writing Chinese text, where this company is referred to. Is it the case, that I would have to choose different representations for "Blablawabla", depending on whether the text will be read by Mandarin or Cantonese speakers? Or are there some "standard" characters that are pronounced very similarly in Mandarin and Cantonese and I have to be aware of them when transliterating? Or am I misunderstanding the idea completely?