While the original idea of the layout was to be British in general and Yorkshire in particular, I had to develop the ideas to be mutually compatable between the 3 countries for which most of my stock is based. As German locos can run in to Switzerland it was just trying to work out the scenarios to justify (invent) the line.
There would also be passenger flows to and from the various stations. These would be served by local stopping trains and also international and national expresses. Freight flows would be of a similar nature.
As it is a major anniversary of the line and in real life the Channel Tunnel has been built, don't be surprised at whatever is running on the line. For the stock list see the relevant page.