GNU/Linux Elementary OS Installing Broadcom BCM4321/BCM4322 Driver Guide
How to Install Broadcom BCM4321/BCM4322 Wi-fi/Bluetooth Driver on Elementary OS 0.4-Loki/5.0-Juno/5.1-Hera LTS GNU/Linux – Step by step Tutorial.
The Package Provides the Source Code for the wl Kernel Modules and makes use of the DKMS Build Utility to Install them for the Running Kernel.

GNU/Linux Elementary OS Broadcom BCM4321/BCM4322 Driver Installation Guide