If I win map role am I allowed to choose my opponents map?

This sounds like a house-rule question.

Barring added rules, there are no rules about what map can and cannot be used outside of Modern Age.

Some venues and events have you choose a certain number of maps that you are using - in which case you couldn't choose a map that was not on your list.

You could always have the person who lost the map roll be player 1 and then they would pick map.

I hope that helps.