This isn't a gift card deal, per se, but it's kind of related. I first encountered this Capital One Shopping deal during Target Circle week. At that time I was able to stack it with a 20% Target Circle offer for a seriously incredible discount on party tickets and 3-day park tickets. I received the Capital One Shopping offer again this week.
I suspect that the way to trigger this offer is to install the Capital One Shopping applet in your browser and log into your account, then visit TripAdvisor and browse activities. I searched for Disney park tickets, added them to my shopping cart, but then didn't check out. One or two days later I received this Capital One offer in my email - 21% back on Capital One Shopping. This isn't cash back - Capital One rewards must be used to purchase gift cards, and there may not be an option you value, or you might have otherwise purchased it at a discount, but it's still a very good deal. Also, tripadvisor doesn't sell every possible Disney ticket - for WDW, I believe they only sell 3, 4, 5, and 7 day tickets, and party tickets. They also sell DL tickets.