I purchased my unlocked iPhone SE directly from Apple. I've got just a "pay as you go account" with Telus. I can't justify having a full blown account paying upwards of $80/month or more as I don't use my phone for a lot other than making a few phone calls monthly, texting now and again, rarely if ever use any online or data services outside of my home. I'm planning a trip to New Mexico, USA in February & was wondering how or if I'll be able to use my phone to make calls with my existing "pay as you go" account.
Telus Pay as You Go accounts do not allow use in the USA, except 911 calls. You could purchase a SIM from a supplier in the US for your stay, but, of course your number would change. If you have a small number of contacts whom you can share your temporary number, this would be the easiest option - just confirm your phone is unlocked and pick up a new SIM at a location near your destination. If your phone was purchased after December 2017, it will already be unlocked; else you will need to contact Telus to have it unlocked.
You cam also FaceTime and iMessage with other iPhone users on Wi-Fi.
Telus' subsidiaries Koodo and Public Mobile each have prepaid accounts which offer the option to purchase US roaming for your stay. You could port your number to either, if remaining on prepaid is important for you.