OHIP can be your insurance but a lot of people did not recommend it because it is an insurance from Canada. This could conflict with getting through the immigration officer at the airport or even have a problem when trying to get your permanent resident card because they see how much can your insurance cover and what does it cover. On the other hand, Study and Protect is a private irish insurance for students. They also have a designated insurance for medical students too at an Irish university.
This is the link, and you can get a quote and then they will offer you the type of insurance you want. That depends on your personal preference
Medicover
I will definitely go with Study and Protect insurance because its just around 150 Euros a year and it is much better than getting a private insurance from Canada because it is easier to deal with when you're in Ireland and requesting your permanent resident card.
NOTE: This insurance includes many colleges such as mine (UCC) but does not include NUIG. I would suggest looking or emailing them if you can still use their products.
EDIT: Good news, check this link from NUIG website where they do say you can get Study and Protect "
Tab 4 Content - NUI Galway "