I think it's about the size of Yorkdale Mall. I know the parking lot can hold 6000 cars (Heard that on the radio today) and they've also mentioned that this will probably be the last mall that we'll see in ages.
There's a current trend of going big box stores like you see around the big movie theatres.
I remember a time when going to Wonderland seemed like going to the outer skirts of the GTA, but it's all developed and shit now. Gotta love the urban sprawl.