Yes, you absolutely can. Since you have a Canada-US-Mexico plan, your phone functions essentially the same way regardless of which of those three countries you are currently standing in. You can call and text your friends in the US without any extra charges. You can also call or text back home to Canada or to friends in Mexico at no additional cost. All incoming calls and texts from anywhere in the world are included. Make sure this is toggled ON in your phone's cellular settings so your data works. Your phone should automatically connect to a partner network like AT&T, T-Mobile, or Verizon. If you have trouble, you can manually select one of these in your "Network Selection" settings.
You might receive an automated "Welcome to the US" text from Public Mobile suggesting you buy a roaming add-on—you can safely ignore this, as your plan already covers your usage!
EDIT: One note to add, not all phones will work in the US. In case you have issues, since we don't know what phone you're currenty using, you can check the VoLTE checker to confirm your phone will work there.
https://www.publicmobile.ca/en/get-help/articles/volte
