Hi,
I am from Ottawa, and I was exactly in the same situation as the original poster. For me it was cheaper to rent a car for an additional month until I got the G license, than to pay G1 based car insurance for my own car. I needed to wait about a month here in Ottawa to get a G test appointment. Some colleagues from my office scheduled their G tests in smaller neighbouring towns where you do not wait so long.
You can rent the car with the license from your home contry and you can use in the G drive test without any problems.
I also scheduled two times two hours of driving lessons with the local instructor, to familiarize with the local pecularities.