During my CBR stays and visits, I've seen most buses start at Jamaica 1st, then Aruba, Barbados, Martinique, OPR, Trinidad North and Trinidad South. The other route is Martinique 1st, OPR, Trinidad North, Trinidad South, Jamaica, Aruba and Barbados. Hope this helps!!
I've stayed at CBR twice and it seemed that the bus took a different route each time, depending on which park they were coming from or going to! It really only takes a few minutes to circle the resort.