Some organizations in Canada have an official preference for hiring Canadian citizens, and say so in job announcements. If one is a Canadian citizen but also a U.S. citizen, does that mean one would be treated differently from a candidate who is only a Canadian citizen?
It is illegal to discriminate on the basis of "national or ethnic origin"
This is spelled out in the Canadian Human Rights Act s3(1).
However, a person's citizenship is something that can (must) be discriminated on. Unless it is being used as a proxy for "national or ethnic origin".
Right to work in Canada
To be allowed to work in Canada, person must be a:
- Canadian citizen (including dual-nationals),
- non-Canadian citizen and hold a work-permit,
- non-Canadian citizen and be doing exempt work.
So, an employer asking about citizenship to determine eligibility is fine. An employer asking to discriminate in favour of group 1 over group 2 or 3 is not.
Employment and human rights law are mostly provincial if the employer/service provider is not federally regulated.
Federally regulated sectors are out of provincial jurisdiction with respect to employment and are subject to the federal Acts (Canadian Human Rights Act, Canada Labour Code) instead.
Citizenship is a enumerated protected ground in Ontario. Employment decisions cannot be discriminate on citizenship (e.g. requirement to have Canadian citizenship) unless a legal requirement exists. Certain general exceptions apply, e.g. essential job duty or business requirement, certain social/cultural/religious organizations.
Some organizations in Canada have an official preference for hiring Canadian citizens
This in itself could be illegal (if they are subject to Ontario law).
If one is a Canadian citizen but also a U.S. citizen, does that mean one would be treated differently from a candidate who is only a Canadian citizen?
This would also be illegal.
If the job requires security clearance or work eligibility in the US, dual citizenship can be taken into account at that stage (for better or worse).
Citizenship is also often closely related to national origin or ancestry which is a protected ground in all provinces and federally. Even if your particular citizenship has no relations with your national origin, it might still be an illegal discrimination.