Do the Glen first, then the Falls.

Yes, you can hit both in one day without rushing. Start early.

Niagara Glen opens at dawn and the trails are cooler in the morning. You’ll beat the heat and most of the crowds. Give yourself two to three hours to hike the main loop and scramble down to the river. It’s proper nature—roots, rocks, stairs. Not a paved stroll.

After the Glen, drive or bike over to the Niagara Parkway and head toward the Falls. By late morning the tourist crush is in full swing, but you’re done with the hard part. Spend the afternoon doing the obvious stuff—Table Rock, the promenade, maybe the boat ride. You’ll have energy left because the Glen didn’t wipe you out in the midday sun.

If you reverse the order, you’ll waste the best light on the Falls crowds and hit the Glen when you’re already tired. Don’t do that.