i think the look of 20% front 5% rear is the best. However, here is Quebecs tint law:
"Quebec - For the driver’s compartment, right and left, the minimum Visible Light Transmittance is 70% on automotive net basis. Any film may be installed behind the driver’s compartment, provided the vehicle is outfitted with 2 exterior rear view mirrors."
So the most you can have and still be legal for the front is 70% the rear can be anything though.