How much data do you need outside of public WiFi that would allow you to use messenger apps like WhatsApp etc? What are the roaming rates of your UK carrier? Using the later would allow you to take incoming calls when UK residents and companies are calling your UK number.
I have family and friends in several European countries (inside and outside of the EU). Up to very recently (with the whole "how much data can we throw at you for CAD35?" madness) their North American roaming plans were, adjusted to exchange rate etc, almost everytime a considerably better deal than using a Canadian prepaid plan.
As mentioned above, while it's certainly possible with some work-arounds, it's not really very convenient any more to sign up for Public Mobile if you are coming from abroad. If you are here for 5 weeks you'd also need to pay for two plan cycles at 30 days.
In terms of technical compatibility, as long as your phone is unlocked and supports Public Mobile / Telus frequencies you should be ok. Be aware that Public Mobile has a very restrictive white list for providing VoLTE to VoLTE capable phones, so your phone will most likely drop down to 3G frequencies for calls.
