I have only had troubles with mudflaps in Saskatoon. But I believe the general concensus to be legal in Canada is the top 1/3 of the tire must be covered horizontially by fender or mudflap from the rear. This is for both front and rear tires. Does this make sense to you? Also, I believe the maximum that a tire can stick out from the side is 1 1/2" without any covering 360 deg., this is up to discretion of said cop.
I've seen guys running around with 2-3" sticking out with no real problems.
FYI, keep you truck clean - wash it, keep your windows and lights, licence plate clean and you won't attract attention, showing respect for some rules seems to allow bending of others.