not really true. You feel that cantonese is more commonly used because you live in either KL, Ipoh and some other place. You have to remember KL is a small place in Malaysia and speaking of "commonly used dialect", you need to have a wider view. To be more exact, there is no single dominant chinese dialect in Malaysia. This depends on which area you are living in.

In SG, it is unlikely for you to find someone who can understand cantonese except when they are actually Malaysian, Hong Kong ppl or some really elder Singaporean. If you speak cantonese in JB, most of them will give you a stare, "har?". Mandarin is now the de facto language used in JB among chinese community due the influence of Singaporean media.