Could I be able to join Caribbean medical schools after finishing my grade 12 in Toronto.?

Yes, you can do a premed program in the Caribbean, complete the medical school at the same school and be eligible to be licensed in both the US and Canada.  But you need to be very careful.  The first thing you need to do is check with the state licensing authority (in the US) where you might be interested in practicing.  Each state is the final arbitrator of whether you can obtain a license to practice medicine.  Many states have minimum education requirements and bypassing college might disqualify you.

You also need to be very careful about which Caribbean school you attend.  The top 4 schools are accepted very well in the US and Canada.  The rest can be problematic for you when it comes time to obtain a license.  The best schools offer US federal student loans (use this as a benchmark, as most of the schools are able to get Canadian loans).  You should also visit either StudentDoctor.net or ValueMD and talk with current students at any of the Caribbean schools.