Can I just show up and hike?

You cannot “just show up and hike” the entire trail if you do not have permits. You can however do some sections of the trail with no, or few permits, such as Section B (you will still need an Alberta Public Lands Camping Pass). There are other sections that are also possible with just a Public Lands Camping Pass, and easy to book random camping permits, such as Section D, F, and G.