The question has two parts: (1) How many above ground parking
structures are there in the snow belt of the U.S. and Canada?  (2)
Does TreCan ( a Canadian company that makes snow melters) have any
competitors?  A competitor would be someone who could, for instance,
melt the snow off the top of a parking structure (as opposed to
melting the snow off of a driveway or sidewalk)

Sounds like an aircraft de-icer

If its a new structure, you could possibly install radiant tubing on
the exposed story, thus melting the snow as it hits the ground.  I
would contact a company called Wirsbo (Wirsbo.com) and ask them about
it - in their literature they only reference driveways and sidewalks
but I know that their good sized parking lot in their facility in
Minnesota is radiantly heated (although it isn't a parking structure).
 As far as existing structures, I'm not sure how practical a retrofit
to radiant would be.

This is probably not the direction you wanted to go, but I saw
snowmelt and this popped into my mind.