canu means 'singing, to sing' but is is also used for 'playing, to play' when a musical instrument is played - mae hi'n canu gitar 'she is playing the guitar'.
So 'canu gwerin' means 'folk singing/playing' , which is usually translated into English as 'folk music'. A lot depends on context though, and you can always add other words into a phrase to make it more specific:
- Wyt ti'n hoffi canu caneuon gwerin? - Do you like singing folk songs?
- Wyt ti'n hoffi canu cerddoriaeth werin? - Do you like playing folk music?
- Wyt ti'n hoffi gwrando ar ganeuon gwerin?