i would guess its pronounced rox-eh-lahn-ah. i've learned that Turkish words dont have any silent letters (at least thats what a Turkish friend of mine told me) so if you see a letter in there (like the E in the middle), pronounce it.
If you want to stay with a Turkish name all the way through you could go with:
Roxelana Yasemin (yass-eh-meen, this is the name of my friends daughter)
Roxelana Ayse (ay-shuh)
Roxelana Nur (noor)
Roxelana Busra (bush-ruh)
Roxelana Semra
Roxelana Esra
or Arabic mn's
Roxelana BasimaRoxelana BasiraRoxelana Fayruz (fair-ooz)
Roxelana Hadia (hah-dee-ya)
Roxelana HafsaRoxelana LeilaRoxelana Lujayn (loo-zhayn)
Roxelana NadiaRoxelana Rabia or Rabea
Roxelana RajaRoxelana Sadia or Saudia
Roxelana SafiyaRoxelana SamiraRoxelana Shahrazad - this one is a bit of a mouthful but it kinda sounds cool.
Roxelana TalibaRoxelana ThaminaRoxelana ZaynaRoxelana ZainabRoxelana Zuleika
hope this helps! :)