I know that Ontario has similar provisions for 'insecure load' in s. 111(2) of the Highway Traffic Act and a $130 fine:
"No person shall operate or permit to be operated upon a highway a motor vehicle that carries a load or draws a vehicle that carries a load unless the load is loaded, bound, secured, contained or covered so that no portion of the load may become dislodged or fall, leak, spill or blow from the vehicle."
http://www.huffingtonpost.ca/2016/01/20 ... 29934.html
+++ This is not legal advice, only my opinion +++
There are sections (s.74) that say you need a clear windshield, clear side windows, and a clear view to the rear (either clear mirrors or a clear back window).
Nothing specifically says you need to remove snow from your roof or trunk for example. There was a bill before the legislature to create a specific offense for not clearing snow from a vehicle... it got through a few readings but it was never added to the HTA (maybe killed by an election call?).
But there are situations where snow on a vehicle is clearly unsafe, and officers stop these vehicles... in regards to charges, I have heard of ones like the insecure load... or unsafe vehicle... or even "deposit snow on roadway" (s.181... meant for people shoveling snow onto the road). These charges are all shoe-horned into the situation so it would be up to a JP to decide if they got that far.
Definition in the HTA or Dictionary?
But you have to stop and think, how many times have you been driving on the highway and another driver is too lazy to clean the snow off their car and it blows all over and creates whiteout conditions?
If you get stuck behind one you certainly understand that it creates dangerous situations.
I have seen people drive with only a small section of their front windshield cleared and no peripheral vision, this made them make a right turn at a red light cutting me off and I nearly rear ended the guy, guess who would have been at fault? Me, even though I was going through a green light, he could not see me coming from his left.
I guess the officer just wanted to make a point of "clear all the snow off your car before you put it in drive" and got creative with it.