If you're visiting Canada with a GSM unlocked iPhone 5, you have several Pay As You Go, or prepaid, options to consider. Nano-SIM availability is still hit and miss. There's not reason you shouldn't be able to get one, since every major carrier and subsidiary is currently carrying the iPhone 5. However, getting them to give you one for short-term PAYG might be a battle, or could incur an additional charge.
Canadian carriers like Rogers, Bell, and TELUS all have discount subsidiaries, namely Fide/Chatr, Virgin, and Koodo, so we're going to focus on those. Other carriers, like Moblicity, Wind, and Videotron use AWS frequencies (like T-Mobile in the U.S.) and don't currently support the iPhone.
If you’re visiting the United Kingdom with a GSM unlocked iPhone 5, your main options for Pay As You Go SIMs are limited to two of the five major networks. At the time of writing, only Three, T-Mobile and O2 offer nano-SIMs on Pay As You Go (pre-paid) deals.
Read on for a breakdown of what you can expect, as well as a few other options you may want to consider.