@Aethelbald Anyone in the world*

* with a mobile phone
* who is a resident of Canada (no, you don’t even need to be a citizen, just a permanent resident in Canada)

from the liberals bylaws:
https://liberal.ca/wp-content/uploads/sites/292/2020/09/by-law-4-2.pdf
To be eligible for Registration in the Party, a person must:
(a) be at least fourteen (14) years of age;
(b) support the purposes of the Party; [duh]
(c) ordinarily live in Canada or, for Canadians living abroad, be qualified as an elector who may vote in accordance with part 11 of the Canada Elections Act; [slightly more broad than the above strictly speaking but probably legal]
(d) not be a member of any other federal political party in Canada; and
(e) while Registered as a Liberal, not have publicly declared an intention to be a candidate for election to the House of Commons other than as a candidate of the Party