Hiking in terrain you will be hiking in is the best. Not always practicle. Any hiking/walking will help. When I was training to hike the PCT I lived on Nantucket Island. Highest point was just over 100'. I would normally bike into work & walk home with a ten - 15 pound day pack. Only three miles each way but bike ride kept me in areobic shape & the hike home worked on my legs even more. I did get a short traing hike in befor I hit the trail where it was 18 miles to the first reliable water.
In short: if you can't train in actual conditions, train in a way to build what you need for them. Backpacking is mostly mental. then comes legs & lungs.
In short: if you can't train in actual conditions, train in a way to build what you need for them. Backpacking is mostly mental. then comes legs & lungs.