Interesting situation indeed. With Canada being on-shored, I believe all Canadian based CX pilots must have citizenship or the right to live and work in Canada. As the Canadian CX pilots now work for CX Canada the following does not apply. I guess that's why CX direct deposits into US bank accounts of Canadian based pilots who don't have the right to work in Canada.
Canada Immigration and Refugee Protection Regulations (IRPR)
Division 3
Work Without a Permit
No permit required
186. A foreign national may work in Canada without a work permit
(s)
as a member of a crew who is employed by a foreign company aboard a means of transportation that
(i) is foreign-owned and not registered in Canada, and
(ii) is engaged primarily in international transportation;
As the US is presently not on-shored my understanding is that Canadians can still be based on US bases as they are employed by a Hong Kong company under a similar rule. However if CX will on-shore the US I believe a green card will be required.