It would be too early to give any verdict as Mercedes-Benz GLA 2020 is not launched yet. So, we would request you to wait for its launch so that we can share the fruitful comparison.
Volkswagen Tiguan Allspace is still available for sale and for the availability, we would suggest you walk into the nearest dealership as they will be the better people to assist you because it depends on their stock book. You can click on the following link to see the details of the nearest dealership and selecting your city accordingly - Car Showrooms.