If there is a park, I echo neuhaus' comment that the connections north are key. How about a pedestrian bridge OVER the Gardiner that connects this space to the future Copeland Transformer park. Make it a landmark destination with a lookout where you can view the water to the south, downtown to the north, and the traffic down below both east and west. Create stepped seating like Highline's 10th Avenue amphitheater. (See image attached).
With that being said, with the future improvements to the former York offramp area, the Jack Layton Ferry area overhaul, and the other parks going up near the waterfront, do we need another park here? If I'm down by the waterfront, I'm going to head to the waterfront and not next to the Gardiner. Instead, build a landmark and create a pedestrian bridge is the way to go.
Place the landmark building at the west side of this site than have my proposed bridge going from eastern side of this site northeast over the Gardiner to Copeland Transformer area. Would truly have wonderful views of HTO Park and the water to the South and connects very nicely with the elevated Copeland Transformer area on the North side.
Here is a rough 360 degree view from the Gardiner of HTO and the downtown...
https://www.google.ca/maps/dir/43.6...4!1sUMv4LjIURz3TnqKY_Js3gQ!2e0!7i13312!8i6656