Which bachelor’s degree, mathematics, economics or business administration, is generally considered more advantageous for pursuing a master’s degree in finance abroad?
As a simple rule of thumb I would go from the more technical toward the less technical so my choice would be mathematics.
All about the same, you could look up a few prospectuses for courses and universities you are interested in. If they indicate a preferred undergraduate background, go for the one that is indicated. If not, the most advantageous will be the one that you enjoy the most.