I just asked the place that tinted mine, and they've used 35% on the front two windows and 15% on the rest.
35% is the legal limit on the fronts in Ontario. Other provinces like Quebec don't even allow tinting.
First off, hello all! First post - I am strongly considering a purchase of the CT in the next couple of weeks.
And not to seem condractictory right off the start, I don't believe that Ontario has a "legal" limit...
Colour coating obscuring interior
(3) No person shall drive on a highway a motor vehicle on which the surface of the windshield or of any window to the direct left or right of the driver's seat has been coated with any coloured spray or other coloured or reflective material that
substantially obscures the interior of the motor vehicle when viewed from outside the motor vehicle. R.S.O. 1990, c. H.8, s. 73 (3).
Windows to afford clear view
74. (1) No person shall drive a motor vehicle upon a highway,
(a) unless the windshield and the windows on either side of the compartment containing the steering wheel are in such a condition as to afford the driver a clear view to the front and side of the motor vehicle; and
(b) unless the rear window is in such a condition as to afford the driver a clear view to the rear of the motor vehicle. R.S.O. 1990, c. H.8, s. 74 (1).
Application of cl. (1) (b)
(2) Clause (1) (b) does not apply to a motor vehicle that is equipped with a mirror or mirrors securely attached to the motor vehicle and placed in such a position and maintained in such a condition as to afford the driver, otherwise than through the rear window, a clearly-reflected view of the roadway in the rear or of any vehicle approaching from the rear. R.S.O. 1990, c. H.8, s. 74 (2)."
Like so many traffic laws, I think it's left to the discretion of the officer.
In any case, I'm sure 35% would be an acceptable limit (my car now being 35% all around with no issues yet)... even though I have had friends with lighter tint be issued a "repair" ticket or whatever it's called.
I can't see most cops would give a hard time to a lexus-hybrid owner with 35% tint

but you never know.