Connecting to CanBus is not that onerous John. You tap into back of OBD2 plug. You need +12V, Ground, Can High & Can Low, connected to decoder to give speed pulse output.

I would be concerned using GPS to control speed as you would loose signal when satellite coverage is lost, in cities, tunnels etc.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone