Flight turnover

No, you must wait in the terminal for the next flight. They “clean” the plane between flights.

Toronto (YYZ) Varadero (VRA)
via Santa Lucia (Camaguey)
Departing: Tue Oct 02 2018 4:15 PM
Arriving: Tue Oct 02 2018 9:50 PM

Varadero (VRA) Toronto (YYZ)
Departing: Tue Oct 09 2018 10:35 PM
Arriving: Wed Oct 10 2018 1:59 AM
1 ticket: 1 adults

but i will be getting on the same plane .. right

Where is the stopover? The info you posted looks like a nonstop flight. But even if it is a through flight on the same aircraft, you will have to deplane with your carryons for an international destination and reboard 30 minutes prior to departure. The crew has to do a complete security check for all internationally bound planes, so it has to be empty. On domestic flights, there could be a number of reasons to need the plane empty between flights, such as they have a crew change, or they need to clean and cater the aircraft. Also because they aren't getting paid when the aircraft door is open so that's their only break time to eat and relax for a minute.

Santa Lucia (Camaguey)

its in cuba then to varadero