Very much enforced, in certain areas, (normally it is the S.A.V.E team out of Orillia doing the enforcement, especially on long weekends). But normally only if the driver is doing something stupid. There was a fellow charged last season outside of Bobcaygeon. He was ticketed for:
1. Speeding, (the limit on the road he was travelling was 50 km which means ATV's are limited to 20km/h, (because this is road is a main connector road from parking to trails it is actually signed at 20 km/h for ATV's).
2. TWO tickets for carrying a passenger, (he had his adult son as well as his grandson, on the bike with him)
3. No helmet, (the son and grandson had helmets)
I believe it was just over $900 in fines by the time he walked away.
The new regulations, (134/15 & 135/15) simply permit, (with a local bylaw permitting their use), 2 up atv's, (those FACTORY built to carry a passenger), and "SOME" UTV's, (Side by Sides), to now use roads which have been approved by the local bylaw.
These new rules come "into effect" as of 01 Jul 2015,BUT thta doesn't mean you can use your machines on the road beginning that day, If there is an ATV club in the area you ride they will be applying to the local council to pass the amendments to their bylaws, (this isn't likely to happen by 01 Jul). So until the bylaw is passed you still risk a ticket.
NOTE not ALL side by sides are permitted there are size and CC restrictions.