I will second the Trek over the top!!!
That said, how old is your son, and are you bringing sleds or need to rent?
Do you want to ride trails, climb mountains, travel distance, party at night, hunt where you go???
Feed more info and we can get more specific about stuff.
One caution about the Irondog- some years the trail sucks, and is more of an endurance ride to thrash sleds. The Trek is more groomed than not, but is only a weekend.
Another event wold the the Alcan 200 if you like speed. It is here in Haines, we get the highway closed for 100 miles that day and race on the road. Good time with a lake race the next day.