My AAA doesn't offer Niagara discounts, either. In looking at the Adventure Pass on Sam's Club it includes this:
Admission to: Journey Behind the Falls, Maid of the Mist, Niagara’s Fury and White Water Walk. Plus Bonus coupons for discounts to: Butterfly Conservatory, Whirlpool Aero Car, Sir Adam Beck Power Tour and 1812 Heritage Sites.
On the Sam's Club site, I put Ontario, but this is the only pass that shows. It has Maid of the Mist instead of the Hornblower Cruise. Narnia_girl, did you purchase this pass? Did the voucher list Hornblower? To my understanding Maid of the Mist is from the US side.
I checked again and made sure I searched Niagara Falls, Ontario. Here is the full listing from Sam's Club. It looks like in the first paragraph they do say Maid of the Mist, but in the details they say Hornblower.

I have not bought this yet; I'll try to call them tomorrow, but I think it is the Canada side.
Niagara Falls Adventure Pass
Discover a whole new side of Niagara Falls through world-class attractions: Journey Behind the Falls, Niagara's Fury, White Water Walk and more!
Highlights / General details
Niagara Falls Adventure pass lets you experience, feel and hear the Falls from all perspectives, providing Admission to: Journey Behind the Falls, Maid of the Mist, Niagara’s Fury and White Water Walk. Plus Bonus coupons for discounts to: Butterfly Conservatory, Whirlpool Aero Car, Sir Adam Beck Power Tour and 1812 Heritage Sites.
Journey Behind the Falls: Take in spectacular views from observation decks at the foot of the Falls where you can actually feel the thunder of the crashing
waters. This exhilarating journey takes you down 150 feet below the heart of Falls
through tunnels that lead you behind the rushing wall of water.
Hornblower Niagara Cruises: Come Explore the Roar by sailing into the mist and crashing waters of the thundering Falls. No trip to Niagara Falls is complete without experiencing the thrill of the Falls.
Niagara’s Fury - The Creation of the Falls: Travel back in time 10,000 years to experience the Creation of the Falls. Be entertained by the animated pre-show then enter a specially designed 360 degree theatre, where you’ll witness the power and beauty of nature in 4D as the history of Niagara is revealed. You’ll feel like you were actually there when Niagara’s Great Gorge was formed!
White Water Walk: Take a walk like no other along a boardwalk at the very edge of the world’s wildest stretches of whitewater! After travelling down 230 feet to the brink of the rapids, you’ll marvel at the relentless power and beauty of nature as you walk along 1000 feet of whitewater rapids. Trillions of gallons of water are forced into this accelerating trough – a sigh that will take your breath away!
Butterfly Conservatory: This magical attraction features over 2,000 colorful tropical butterflies floating freely among lush, exotic blossoms and greenery. Paths wind through the rainforest setting, past a pond and waterfall and the Emergence window, where butterflies leave their pupae and prepare to take their first flight! The self-guided walking tour of the Butterfly Conservatory begins with a short, informative video presentation that is close captioned for the hearing impaired.
Floral Showhouse: For over 60 years visitors have come to Discover Paradise at this lush oasis, just a short walk from the Niagara Falls. Collections of orchids, succulents and other tropical plant species are on display throughout the year, along with floral shows that reflect the changing seasons. Flying throughout the greenery are colorful tropical birds that may sing for your entertainment!
Inclusion
Classic Pass: Admission to Journey Behind the Falls, Hornblower Niagara Cruises, White Water Walk, Niagara’s Fury plus optional two days transportation on the WEGO bus system. (Bus only runs along the Niagara Parkway.)
Nature Pass: Admission to Journey Behind the Falls, Hornblower Niagara Cruises, Butterfly conservatory, Floral Showhouse plus optional two days transportation on the WEGO bus system. (Bus only runs along the Niagara Parkway.)
Exclusion
Transporation to and from the attractions; Gratuities (optional).
Hours of operation
Available: Daily, May 1 to November 15; Bus runs every 15-20 minutes depending on traffic.
Duration
Approximately 1 day.
Location
Table Rock Welcome Centre, 6650 Niagara Parkway, Niagara Falls, Ontario.
Additional Information
All attractions are wheelchair accessible.
Policies
Should the Hornblower Niagara Cruises not be sailing the Whirlpool Aero Car will be substituted.
Lower observation deck closed due to winter conditions approximately December 1 to mid-April.
**All information requested must be supplied or booking is subject to automatic cancellation**