We already have underwater tunnels for trains, such as the one between England and France - water would come crashing in regardless of whether there is air or a vacuum in the tunnel.
It's not actually Futurama, the tunnel won't be train-sized and made of glass.
Surely any tunnel built will be surrounded with rock/concrete as its structure, ultimately it will still be a case of people surrounded by solid material surrounded by water.
They aren't going to dig a tunnel through rock all the way underneath the Atlantic - that's many times further than the Chunnel, and that was a serious undertaking. The article implied it'd be underwater.
The tunnel itself will be formed of solid material, they don't need to go underneath the sea bed they will put their own construction in. That is what the tunnel will be, it's not just a vacuum in the middle of the water.
It's not actually Futurama, the tunnel won't be train-sized and made of glass.