Telus is stronger out west but they share towers with Bell. If you were fine with Telus then you'll be fine with Public Mobile (PM). Seeing as how PM belongs to Telus.
Publicmobile uses the exact same cell towers as telus, service should be exactly the same. As for data, if you get 3G it is slightly slower than LTE, but not noticeable for me. The 3G is actually just throttled LTE rather than true 3G.
I am in Newfoundland and service is absolutely fine for me. As stated above it runs off Telus and your service should be as good as Bell or Telus. What part of Newfoundland are you in?
Forgot to address your question about transitioning from Telus. First of all if you were on Telus then your phone will definitely work with Public Mobile, even if it's locked.
When I transferred from Telus, after I ported my number and finished the activation process, everything worked perfectly less than a minute later.
Public Mobile is a Telus-owned brand, and as thus, uses the exaxt sane netwotk. So, there will be no difference when it comes to that if coming as a customer from Telus. The only differences will be on retail prescense, customer service, and in plans and pricing.