Bose launched its QuietComfort 35 II noise-cancelling headphones with Google Assistant last year. Today the company has finally added support for Amazon Alexa Voice Assistant via update.
Once updated, you can change the action button to launch Alexa (app should be installed on the phone and configured for it to work) instead of Google Assistant or use it as a noise cancellation switch. You can change this in the Bose Connect app settings.
The latest update to Bose Connect app 6.2.2 along with new firmware update (v3.1.8) enables the feature. The update also includes fixes and enhancements. The firmware update that takes few minutes to push to the headphones.