This paper describes our recent investigation on the use of both intra-syllable and cross-syllable acoustic units for Cantonese text-to-speech synthesis. In our previous work, isolated monosyllable units were used for concatenative speech synthesis of Cantonese. The synthetic speech was considered to be unnatural in such a way that there was an obvious lack of perceptual continuity. The proposed system adopts an acoustic inventory that covers all legitimate intra-syllable and cross-syllable acoustic units. Synthetic speech produced via concatenation of such sub-syllable units better captures the pertinent transitory effects that are crucial to perceived naturalness. Different strategies are used to concatenate speech segments with different acoustic-phonetic properties. Subjective listening test shows a noticeable performance improvement that is accounted for mainly by smoother transition between sonorant segments.