Sorry for reposting this rendering, but it is a bit deceiving in terms of relative location to the mall. The mall parking deck they are showing (mall employee parking) with the "Yorkdale" sign is actually quite a bit north by the movie theatre. South of that parking deck is where the mall's next expansion is currently under construction (former TTC commuter lot and mall parking). Further south is the office building and GO Yorkdale station, Yorkdale Rd. and S/B Allen Road on-ramp, Yorkdale Park, and finally we get to Ranee Ave. And I don't believe GO buses travel on Ranee, they make use of the Allen Rd. underpass at the north end of the Yorkdale subway station to get on the 401.
Rendering artists do use a bit of creativity when creating marketing promotions, yes, but I had to raise my eyebrow at this one. It's making it seem like walking from the condos/Lawrence Heights to the mall is a quick and easy stroll. As I42 mentioned, the easiest and most comfortable way to walk would be through the subway station (w/ a Metropass). It is possible to go through the park and along Yorkdale Road to a mall entrance (as I type this I'm looking at the path through Yorkdale Park from the office building). Unfortunately it is quite a hostile environment for pedestrians, with narrow sidewalks, tall walls/fences, and fast vehicles who don't pay nearly enough attention towards pedestrians.
The mall is close, but not a simple "walk in the park" to get there.