Unless you go through the effort to split out all your tasks into projects, massage them into a format that DT will understand, and then one by one import these through, activate google tasks sync for the desired project, deactivate, lather, rinse, repeat. There is no task import, except via Google Tasks, so import is out. Bubble interface is fun if you have 10 tasks, and list interface clearly takes second seat to the bubble interface - no grouping, no filtering. I can not recommend it in its current state. Needs to work on the basics before it is actually usable. Also, moving tasks around in GCal through eM Client causes task duplicates on every change.
Many of the projects below will say "we have sync! Just use Zapier/IFTTT/etc", but that is invariably only one-way, create-only sync, so any update on either side and the registration will diverge, which makes sync sort of pointless. I am still actively testing the other options as they progress (or as new options become available) GQueues is basic but hits on all the required points, even if it isn't flawless. One product consistently comes out on top: GQueues.