While this set of Cantonese initials are not present in Putonghua, it is in fact identical to the ‘initial + medial’ combination found in Putonghua [gu ku].
1. The Cantonese /gw-/ is voiceless (that is, different from the voiced consonant cluster ‘gw’ found in English).
2. The Cantonese /kw-/ is identical to the English ‘qu’ in ‘quad’.
For English speakers, note that the difference between /gw-/ and /kw-/ is, again, one of aspiration. For example, the ‘qu’ in ‘quad’ is clearly aspirated; whereas the ‘qu’ in ‘squad’ is not. Cantonese /gw-/ is identical to the English unaspirated ‘qu’.
Note that some speakers would drop the /-w-/ in Cantonese /gw-/ (/kw-/) under certain contexts. For more, see ‘Language Change in Cantonese - /gw-/ (/kw-/) Pronounced Like /g-/ (/k-/)
As to aspiration, see ‘Cantonese Characteristics - Aspiration’.