Can I ask the candidate's status in Canada when trying to fill a role utilizing a hiring grant?

Tricky. Asking about citizenship and immigration status is risky, even when it bears directly on the applicant’s qualifications for the job. I think the way I would handle it is to just restate what you just told me about the requirements for the position and ask the candidate if he/she is qualified on the basis of that information. It’s pretty indirect, I know, but it avoids the need to ask a direct question about citizenship/residency/refugee status.