There are no specific places where expats live! However most of expats who can afford just choose to live in a bungalow or apartment near the sea. Flic en Flac is the second most popular beach after Grand Baie and its only 30 mins or so from Rose-Hill/Ebene.
I used to live in Rose-Hill and did my studies at Ebene which was well within walking distance. There is a good transport system to link you to the Port-Louis city center where you'll get all facilities.
People from abroad tend to think about travelling distances e.t.c but don't forget that Mauritius is a small island and it takes like 1hr or so to go horizontally across and less than 2 hrs to vertically cross it!
Since Ebene and RoseHill are almost in the middle it doesn't matter where you want to stay depending on how long you want to travel for to reach work.....
The rest is up to u!