For public and private health facility services:
All provinces and territories participate in reciprocal hospital billing agreements in publicly-funded hospitals, so a visit won't cost you a thing. OHIP does not cover payments to private hospitals or private health facilities outside Ontario.
Generally, any services you receive in a private clinic in Canada are not insured and OHIP will not reimburse you upon your return. (Except for the physician component of insured services.)
If you're an inpatient in a public hospital while visiting another province or territory, you are eligible for OHIP coverage for the duration of your hospitalization up to a maximum of 12 months.