If your address and your sister address are the same, then, your sister has to add your name to her policy.
If you are under 25 (and male), you should expect your sister's insurance to go up by1000 (if Toronto, double that amount).
The best, is ask your sister asks her insurance broker/agent. Don't take risk else if there is accident, insurance company won't pay, the worse scenario is accident involves injury.
Also, I doubt youncan rent a car if you have G2 only. (Imagine yourself as owner of car rental company).
The best, is hire an instructor.
Anybody with or without driver license can be owner of a car. A BOSS can buy a car, hire a driver, and insurance policy is having that driver as principal driver. And insurance fee is based on that driver's driving record, age, etc.