You need Public Mobile APN Settings for your device to browse the internet with Public Mobile in Canada or any area. Without the apn setting, you can not send or receive MMS with your Public Mobile.
Setting up your device with the following Public Mobile  Internet and MMS APN Settings...
Public Mobile APN Settings

Public Mobile APN Settings(Basic):

Name: Public Mobile1
Proxy: Not Set
Port: Not Set
Username: Not Set
Password:  Not Set
Server: Not Set
MMSC proxy:
MMS port: 80
MCC: 302
MNC: 220

Public Mobile APN Settings Android:

APN Settings Android

APN Settings

Go to setting option <then> Connections <then>  Mobile networks <then>  Access Point Names <then>
Press ADD

Then fill up like as below...

Name: PublicMobiletrue
Proxy: Not required
Port: Not required
Username: Not required
Password: Not required
Server: Not required
MMS Proxy :
MMS Port: 80
MCC: 302
MNC: 220
Authentication Type: Not required
APN type : default,supl,mms
APN protocol: Ipv4
Enable/disable APN: APN Enabled
Bearer: Unspecified
MVNO type: None
MVNO Value: Not required

Public Mobile MMS APN settings:
Public Mobile MMS APN settings

When you set up Public Mobile APN settings, carefully and correctly enter all the information. Thank you.
Read: How to Increase Internet Speed