Unlimited international texting means that you may text anyone in the world while you are in Canada. If you go outside Canada, then you would need roaming add-on.
As per the previous replies, it is probably less expensive to purchase a local SIM. If you search in Amazon, you’ll find SIMs for UK including Ireland. My aunt and uncle recently went on a tour and cruise and did this. The SIM had a preloaded 12gb and a local number for CAD$32. Not bad, eh? They had service immediately when they got there, so they could use Uber-like services and such, and they could text internationally too. 12gb of data was more than sufficient for the 3 weeks they were there.
