How Japanese read Chinese toponym in WW2?

Really brothers me this question is Japanese still read Katakana honkon (ホンコン) and kanton (カントン) which was derived from European Language and banned by Japanese in WW2 for Hong Kong (香港) and Guangdong (広東) China during the WW2? Or transformed to On’yomi of koutou (こうとう) and koukou (こうこう) for Chinese original Kanji likely reading others Chinese city names?