After the already mentioned GQueues, Droptask, Hitask and Nozbe we can now also add Todoist to the list of task managers that created a successful real-time updating and bi-directional sync with Google Calendar. If all these were technically able to sort this out, why can’t Asana?
Meanwhile, keep an eye on Sunrise replacement KIN Calendar and their public roadmap on Trello - let’s all vote for Asana and hopefully we’ll see an implementation in the near future.