From Ontario as well. We have gone twice in August and once in September. We've worn our normal summer clothing, mostly cotton, and been fine. Flip flops and keens for shoes. If you are leaving in two weeks I would get shoes ASAP and break them in! Don't wait until you are there.
Yesterday I wore denim capris and a lightweight cotton shirt. And New Balance sneakers.
We weren't at the park long, but spent a lot of time indoors.
Just walking from the Backlot Express to Launch Bay in the hot sun, we were sweaty. A Blue Milkshake helped the walk!
Walking from the park entrance to ToT, my son's soles on his Vans started to melt! Both mine and dh's New Balance soles were perfectly fine.
Wear shoes that will be comfortable both wet and dry. It rains a lot in August. Usually it doesn't rain long and it dries up quickly though. But twice in July we got caught at AK in the rain and got wet feet.