trust me... their illegal in both Canada and the United States. I'm not pulling this outta my ass, its coming from someone who has been involved in the sport since I was 7 and have even raced MX at a professional level...
I've been sponsored by numerious tracks and organizations and not a single one would let ANYONE with a 3 wheeler even on the track let alone in the trails because the second they do, they instantly becoming liable and can be charged for allowing them to ride.
Next on their list is the banning of 2 stroke engines over 49cc... hence why all the new 4 stroke designs. They've already stopped making 2 stroke sleds and watercraft.