What are the chances/how do I ensure practicing in Cali after graduating from ROSS School of Med (Caribbean)?

To begin with, no Caribbean medical school is accredited by any authority recognized by the US Department of Education.  The Caribbean medical schools that allege they are accredited are accredited by an authority they formed themselves and the principal reasons were a marketing gimmick and to keep out competition.

That said, Ross University is an excellent school and one of the few recognized by the California Medical Board, which has become the gold standard of recognition for Caribbean medical schools.

Your acceptance into a residency program is based on your USMLE scores, recommendations of the physicians you encountered in your clinical rotations, the recommendation of your medical school, your grades and class standing.  The fact that you graduated from Ross doesn't mean you have to apply to a less competitive residency.  Many of Ross' graduates have been through some of the best residency programs.

You might want to review the Residency Match program and the Scramble to get a better ide of how getting into a residency program works:  http://www.nrmp.org/