Is their a way to ensure random recruits are always of a particular nationality and/or gender?

Solution 1:

Yes to your first question, no to your second.

Filling your character pool with enough recruits to fill your entire starting roster and then selecting the "From Character Pool Only" option will cause the entirety of XCOM to be populated with these characters. Simply pre-generate the characters to be of whatever nationality or gender you wish.

However, this will only effect the start of your game. It is not possible to expand this concept to include "only regions you have made contact with" as the game progresses. Furthermore, even your starting location is random, meaning that you will not be able to know what nationality to choose ahead of time.