Chinese-born Anastasia Lin, 25, says she did not receive an invitation to attend the event, which meant she could not apply for a visa.
But she attempted to travel to Sanya, via Hong Kong, as Canadian tourists are eligible for visas on arrival.
Ms Lin has blamed the apparent ban on her human rights campaigning.
She has criticised the "repressions and censorship" in China and is a practitioner of Falun Gong, a spiritual movement which China deems a cult and has banned.
