Thanks for the clarification on tax treaty. Based on what is the current situation, I see he is not being taxed by Omani authorities and all his taxes are this being filed in Canada.
You may also want to read 'Article 16: Income from employment'. One question: Is your brother-in-law's salary credited to his Canadian bank account? That would change the entire understanding of this situation
No, his salary is credited to his Bank Account in Oman - however, he is transferring money from his account to my sister's account in Canada for expenses.
hat said, however, because he has a 'Oman Resident Visa' which was sponsored by his Omani employer (along with his employment visa), maybe IRCC would consider him as a 'deemed non-resident Canadian'.
One more point is that Omani Residential visa is granted to him because of his employment. These two are not separate. Only because he has a job in Oman, he is legally able to stay in Oman with a residential permit (issued on Employer's name). Thus, if his contract expires or they decide to part ways, then my brother in-law will have to leave the country, or in some cases, move to another employer's sponsorship to stay legally in Oman (but not sure if this really happens as I see this a very rare thing).
Thanks for the clarity and feedback, we too are wishing to have a favorable decision in our case. Hoping for the best.
