Correct. You just need to ensure you have roaming on. If you have problems with data in the USA, change it from 5G Auto on your phone to LTE until you get back.
I had the opposite. Rogers/Fido/Chatr won’t work in the building I work at depending on where I stand (Pen Centre), but no issues with either my PM or Telus lines.
Try restarting your phone and make sure cellular is on 5G auto so that it will switch to LTE if there is a connection issue. I’m in St Catharines and have had nothing but positive experiences since the 5G plans went live.
