1. Is the Pali Canon the only canon in modern Buddhism?
No. Additionally, as far as I know, there are also many versions of the Chinese Canon which contain the Āgamas (parallels of the Nikāyas from the Suttapiṭaka of the Pāli Canon), Mahāyāna sūtras & Vajrayāna sūtras.
There is also the Tibetan Canon which contains the Kangyur (material which is similar to the Chinese Canon) and the Tengyur (Commentarial works, Abhidharma and additional treatises).
2. So would the term canon be completely synonymous with Pali Canon in the context of Buddhism?
Bearing in mind what was said above, no.
3. What is the status of texts such as Bodhicaryāvatāra which aren't in the Pali canon?
That text is present in the Chinese Canon1 & Tibetan Canon2.