They both are individual countries, so they don't face that problem.
> How can we put pressure on EU to do this despite high cost?
If you tax air-lines first, and then use the money to build an alternative, even in the most optimistic scenario, you'll end up in a situation where long-distance travels become substantially more expensive at least for a few years. Climate activists claim that long-distance travels are not a human right, but ironically, free movement is one of the core values of the EU. And making travels more expensive would exclude more people than today from exercising their right as a EU citizen.
The only realistic option to make the switch from air to train a meaningful option for long-distance travels, would be to 'internalize' the environmental costs, i.e. a CO2 tax (or certificates). However, to calculate this in a fair manner, this would become so high, that you would face a tremendous economical recession.
To me, it never made sense to spend so much resources (brain, time and money) to reduce emissions, because we cannot go to zero and we have already polluted the planet. Wouldn't it be wiser to spend all this money to "repair" the damage we've already done? Maybe solar panels with artificial photo synthesis? Or GMOs with a higher rate of carbon storage?