Do I need a visa. I am Canadian and travelling to Australia

I believe that is fine even for return train Guangdong to hk to Guangdong on 24 hr transit visa. The trip is very tight unless in hk you are flying to Australia. If not, I suggest you Transit in hk rather than Guangdong as Disneyland is very close to hk airport, or not go to hk at all.

Guangzhou changes their rules from time to time. Its possible you may be refused the ability leave the airport for stops under 24 hours. If they do let you in you will not be able to leave the Guangzhou region. If you want HK Disney i suggest not staying in Guangzhou and booking a flight through Hong Kong instead.