I like the idea, though, the Marineland property itself isn't all that large, it would be something like a 1/3 of the space I've outlined below:
View attachment 551321
I assume the Welland River as a border here, and that Marineland, any overtly natural area, golf courses, and small isolated industry was fair game; I excluded larger industrial and residential patches of development.
That gets you just over 6.5km2 or about 650 hectares/ 1,600 acres and change.
Now....if you were feeling more ambitious, and wanted farmers and developers to get right ticked off at ya.........we could be draw the lines along similar principles, following the Welland river for a bit and then creating a full connection to Short Hills Provincial Park and Niagara Escarpment:
View attachment 551324
That gets you about 6,100ha or 15,000acres of land.
That's just a smidge larger than Rouge Park in Toronto.