If you are adventurous:
A. Alexa to IFTTT. The 'then' will be a Maker task going to...
B. A Tasker server running on Android phone or tablet in your home.
C. Use the above to trigger Intent tasks, which are direct links into other apps.
You'll have to decipher the intents related to Google Tasks.
If you are less adventurous, you can simply move to Todoist. IMO that is the sane, rational choice. I had to abandon Wunderlist due to lack of Alexa integration... and frankly, the move has been good where simple shopping and to-do lists are concerned.