@Zeroone
Public Mobile uses the Telus (Telus+Bell+SaskTel+etc) network in Canada. They proudly advertise the combined network as "Canada's largest 3G/4G/LTE/LTEA/5G network" and "Coast-to-coast network coverage".
Public Mobile always offers US Roaming add-ons and sometimes offers Plans which include US+Canada talk/text/data. In USA, these use the AT&T and T-Mobile networks.
Public Mobile always offers a variety of Long Distance add-ons which allow calling from Canada to other countries (included countries are specified in each add-on). But you can't use your phone to contact other countries which aren't included in any Public Mobile add-ons (you could call China, Taiwan, Hong Kong, Macau, Japan, South Korea, Malaysia, Thailand, etc; you could not call Vietnam, Cambodia, North Korea, etc). And you can't use your phone to make "roaming" calls from any country outside Canada (and USA, if you have that option).
Public Mobile - and Telus - and every other Canadian provider - has no network presence anywhere outside Canada. The roaming and long distance options they do provide are negotiated/purchased/traded individually between Public Mobile (or Telus or whatever) and their foreign counterpart(s).
"Asia continent" is a pretty big place with many countries. The best option for most travellers is to subscribe to a local prepaid provider and use their SIM card while you're visiting. The better option is to subscribe to a provider like Circles Life or CMLink which is based in an Asian country but sometimes offers plans with unlimited "roaming" to Canada (this would basically give you unlimited calling in Canada and a variety of other countries, but people in Canada would have to dial a "long distance" number to reach you, even if you're in the same room) - the catch is that you have to be a citizen of Singapore or China or whatever to subscribe to those providers and to get those deals.
https://productioncommunity.publicmobile.ca/t5/Announcements/U-S-Roaming-has-arrived/td-p/94947
