Put the two regions(3 and 2) into an array. Then you just setup a counter variable which switches from 0 to 1 (0 = region 3, 1 = region 2. Or vice versa) and order them to go to those regions.
I hope it's clear. I'm too tired to know what the hell I'm writing at the moment.
A unit enters Region 1
If
Random interger between 1-2 equal to 1
Then
Order Triggering unit to move to Center of Region 2
Else
Order Triggering unit to move to Center of Region 3