Was able to find some stuff incase anyone else was curious:
Violations as to number plates
12. (1) Every person who,
(a) defaces or alters any number plate, evidence of validation or permit;
(b) uses or permits the use of a defaced or altered number plate, evidence of validation or permit;
(c) without the authority of the permit holder, removes a number plate from a motor vehicle or trailer;
(d) uses or permits the use of a number plate upon a vehicle other than a number plate authorized for use on that vehicle;
(e) uses or permits the use of evidence of validation upon a number plate displayed on a motor vehicle other than evidence of validation furnished by the Ministry in respect of that motor vehicle; or
(f) uses or permits the use of a number plate or evidence of validation other than in accordance with this Act and the regulations,
is guilty of an offence and on conviction is liable to a fine of not less than $100 and not more than $1,000 or to imprisonment for not more than thirty days, or to both, and in addition the person’s licence or permit may be suspended for not more than six months. R.S.O. 1990, c. H.8, s. 12 (1).
Property of the Crown
(2) Every number plate is the property of the Crown and shall be returned to the Ministry when required by the Ministry. 1999, c. 12, Sched. R, s. 5 (1).
Same
(3) For the purpose of subsection (2),
“number plate” includes,
(a) a number plate bearing a requested number,
(b) evidence of validation,
(c) a permit,
(d) a CAVR cab card, and
(e) an IRP cab card issued by the Ministry. 1999, c. 12, Sched. R, s. 5 (1).
Note: On a day to be named by proclamation of the Lieutenant Governor, subsection (3) is repealed by the Statutes of Ontario, 1999, chapter 12, Schedule R, subsection 5 (2) and the following substituted:
Same
(3) For the purpose of subsection (2),
“number plate” includes,
(a) a number plate bearing a requested number,
(b) evidence of validation,
(c) a permit, and
(d) an IRP cab card issued by the Ministry. 1999, c. 12, Sched. R, s. 5 (2).
See: 1999, c. 12, Sched. R, ss. 5 (2), 21.
Number plates, further violations
No other numbers to be exposed
13. (1) No number other than that upon the number plate furnished by the Ministry shall be exposed on any part of a motor vehicle or trailer in such a position or manner as to confuse the identity of the number plate. R.S.O. 1990, c. H.8, s. 13 (1).
Number plate to be kept clean
(2) Every number plate shall be kept free from dirt and obstruction and shall be affixed so that the entire number plate, including the numbers, is plainly visible at all times, and the view of the number plate shall not be obscured or obstructed by spare tires, bumper bars, any part of the vehicle, any attachments to the vehicle or the load carried. 1994, c. 27, s. 138 (7).
Obstruction prohibited
(3) The number plates shall not be obstructed by any device that prevents the entire number plates including the numbers from being accurately photographed using a photo-radar system. 1993, c. 31, s. 2 (5).
Same
(3.0.1) The number plates shall not be obstructed by any device that prevents the entire number plates including the numbers from being accurately photographed using a red light camera system. 1998, c. 38, s. 2 (1).
Same
(3.1) The number plates shall not be obstructed by any device or material that prevents the entire number plates including the numbers from being identified by an electronic toll system. 1996, c. 1, Sched. E, s. 2 (1).
Offence
(4) Every person who contravenes subsection (2), (3), (3.0.1) or (3.1) is guilty of an offence. 1993, c. 31, s. 2 (5); 1996, c. 1, Sched. E, s. 2 (2); 1998, c. 38, s. 2 (2).
Improper or invalid number plates and cab cards
Improper number plate
14. (1) Where a police officer or an officer appointed under this Act has reason to believe that,
(a) a number plate attached to a motor vehicle or trailer,
(i) has not been authorized under this Act for use on that vehicle,
(ii) was obtained by false pretences, or
(iii) has been defaced or altered;
(b) evidence of validation of a permit displayed on a motor vehicle,
(i) was not furnished under this Act in respect of that motor vehicle,
(ii) was obtained by false pretences, or
(iii) has been defaced or altered; or
(c) a permit carried by a driver of a motor vehicle,
(i) was not authorized under this Act in respect of that motor vehicle,
(ii) was obtained by false pretences, or
(iii) has been defaced or altered,
the officer may take possession of the number plate, evidence of validation or permit and retain it until the facts have been determined. R.S.O. 1990, c. H.8, s. 14 (1).
So it seems from this part of the hta that to get an obstruction ticket it does infact have to be obstructed at the time. Although it seems possible they could try to ticket you with the other section where "altered" plate is mentioned. As long as it is visible and the metal plate itself (not its mount/cover/etc) is not altered I cant see you being able to be convicted on this although I could see a police officer handing out a ticket anyway at times.
