How do I set the APN when using Canvas Firmware?

The APN is set in your main.py script.  The script linked below is the minimum modem configuration:

https://github.com/LairdCP/canvas_python_samples/blob/main/networking/modem/modem_minimal.py

This function call is for setting the APN:

https://lairdcp.github.io/canvas_python_docs/canvas_net.html#canvas_net.Modem.set_apn