Jonathan, only gpx files can be imported currently.

TCX files can be generated from our routes. 

Be aware that CT may adjust routes on importation. 

More info here: https://cycle.travel/user/upload_routecycle.travel/user/upload_route

That is SUPER DUPER!

I've uploaded two of my favorite routes created by MapMyRun and converted by Alltrails =

Short bois de Vincennes - Paris

Vincennes Picnique - maison

This (if I understand available to all here) will give some "secret trails" near Paris to all. The park in Saint Cloud is not well known and is closed at night, but now you have a way in the day to cross it. Like Versailles but not touched by anything modern. Incredible. I work there and it took months to figure out how to navigate as some if you make the wrong turn = dead end, or stairs. Even almighty Google and Google Earth do not reveal it.

ENJOY!

Sorry the St. Cloud one is = 

cycle.travel/map/journey/526468

And the other in the Bois de Vincennes, Marne and Seine :

cycle.travel/map/journey/526467

Jonathan, I don't want to be all doom and gloom but I'd encourage you strongly to check that the CT route is exactly the same as the MapmyRun version. 

CT can adjust routes, especially complicated ones, especially off-the-beaten-track ones. Indeed, I'd suggest to anyone to keep the swapping/converting between various apps to an absolute minimum. 

You can use the Trace feature to check the veracity of the CT version. 

As to Google Maps? It is very, very far from almighty when to comes to bike routing. It has its uses but they're rarely to plot a route for a bike.