Encrypt the endpoints!
As the US government showed Google, even if you have private cables and manage the ends, your data isn't safe.
Isn't it therefore now standard practice to encrypt the traffic as soon as it's travelling outside your property? In which case, where's the issue?
As an aside, where I used to work, we had a MOD related network link to Northern Ireland, and that was encrypted because underwater wasn't considered secure, and that was 25 years ago.