I think you need to look at the activity, whether it's a zip line or mountain biking—probably not a good idea—or whether it involves something motorized, and you need to ask yourself whether that is good for the trees. If it's not good for the trees, I don't think it's a good idea.
On the other hand, we want to engage as many Canadians as we possibly can in Canada's first federal urban park, right? I live in Markham, which envelops the northern part of the park, so I am very familiar with it. As a kid, I rode my bike through it.
The question is maybe best answered with a question: What would engage people to the maximum and draw them to the park without damaging the trees? That would be my response. Is that reasonable?