Canadian Visiting Hong Kong and the mainland for a few day

You need a visa to visit PRC for a few days (more than 6 days) and you should apply for it at the CVASC.
Or there is a way for you to avoid the service fee. If you fly to HK from Canada, and then fly to a mainland PRC city which carries out the 72/144 hour free transit, after, you fly back to Canada from there. You can possibly enjoy the free transit in PRC. In this case, you don’t even need to apply for a visa.
So could you please provide your detailed travel plan? And then I can tell you if you need to apply for a visa.

The plan is to take the train from Hong Kong to Guong Dong province stay there for 2-3 days then fly out to the Philippines. Do I still need a PCR visa?

If so, you need to apply for it for your 2 or 3-day travel to Guangdong. If you can take a plane from HK to Guangzhou and then fly to Philippine within 72 hours, you won't need it.