If you study medicine in Ireland you can a) try to get an intern spot after graduation and stay on in Ireland and eventually become a consultant if you are lucky (after 12-14 years) or you can b) write the relevant exams (USMLE for US, MCCEE for Canada, sometimes TOEFL for parts of Canada regardless of where you did your undergrad) and come back to North America for residency (assuming you also meet the immigration criteria for the country you decide to work in ) or c) try to get a training spot somewhere else in either the EU or the rest of the world. Most people from North America who study in Ireland take option b, but some take option a, and a rare few go elsewhere to specialize (option c).
All clear?
Cheers,
M