What is the difference between a port channel and a vPC$?$

A port channel exists between physical devices, and a vPC exists between virtual switches.

A port channel uses data plane traffic separation, while a vPC uses control plane traffic separation.

A port channel creates a single link from several physical interfaces, and a vPC allows port channel physical interfaces to be connected to two different upstream devices.

A port channel uses OSI Layer $2$ and vPC uses Layer $3.$