Often the state regulator, because practice cannot begin without whatever licence or authorization it requires, and that process runs independently. Confirm the regulator's steps first, then work backward. Avoid committing to a start date until both the practice authorization and the immigration route are understood.
Sequence the regulator before the employer's calendar
A licence application can require verification from an institution or a home-jurisdiction regulator, and those third parties set their own turnaround. Start that file as soon as the offer is real. Meanwhile, ask counsel what the immigration route involves for the applicant's specific circumstances. Present the employer with both timelines together rather than agreeing to a date that only accounts for one of them.
Running everything at once looks faster and often is not, because a package drafted before the profession analysis is settled may need rewriting. A professional regulator confirming a licence in good standing works to its own service standards. A provincial licence confirmation depends on a regulator’s own processing. TN bars self-employment, and a Canadian generally seeks admission at a port of entry or may be the beneficiary of an employer’s I-129. The health-care certification and the state licence should be renewed well ahead of the immigration renewal, because an expired certification stops the admission.