Marcus, 29, proposed marriage to the British Columbia native with a customized halo-set diamond ring with a three-carat round center stone at Lynn Valley Canyon in Vancouver, People reported.
"I was trying to find the perfect location to propose," Marcus told the magazine of his May 9 proposal, adding that he met with a local jeweler in Vancouver to design the engagement ring.
"I wanted her to be completely surprised."
Marcus said he took Ally, 35, on a mountainside hike and got down on one knee while walking across a suspension bridge over a waterfall.
Ally's parents and brother were reportedly waiting for the couple with bottles of champagne at the bottom of the river to celebrate upon the couple's return.
"It was truly the most incredible day of our lives," Marcus gushed.
Marcus, who appeared onThe Bachelorette in 2014 and then Bachelor in Paradise's first season that same year, revealed he met his future wife -- who owns a marketing and staffing agency -- through mutual friends at a July 2016 barbecue in Newport Beach, CA.
"The minute I met her I knew this was how you feel when you meet your wife for the first time," Marcus said.
"Ally is gorgeous and strong -- I was completely drawn to her confidence. She's also an incredibly successful business owner, and her business has allowed her the ability to travel. Luckily we met because of one of those work trips."
After meeting on a work trip, Marcus apparently took Ally on their first date to Javier's in Newport Beach.
"It felt as if we had always been together," Marcus told People.
"Immediately we both knew we had found the missing piece in our lives. Ally moved in the very next day! I can truly say I knew I loved her the day I met her. We have moved so quickly because it's always felt so right and meant to be."
Marcus revealed he has joined Ally's agency and the two are "working on big things" together. The couple has also adopted a dog from a kill shelter named Nala, who joins their French bulldog Rocco.
"We're truly homebodies -- we're in love with every minute we spend with our dogs," Marcus said of his relationship with his new fiancee.
"We found our best friends within each other."
Marcus and Ally have already modeled for their engagement photos, which were reportedly shot on May 27 in Jericho Beach, Vancouver.