Laos is the hilly one. The ride from Vientiane to Luang Prabang is about 400 km with 4,300 m of climbing, on paved roads with some dirt and potholes. There is always a support van, so you can sit out a climb when you want a rest.
Buddha Park, then a night in the rainforest on the edge of Phou Khao Khouay National Park. A swim at the blue lagoons outside Vang Vieng. The Plain of Jars, a UNESCO site where thousands of stone jars, thought to be up to 2,000 years old, lie across a valley. Two hard days through the mountains bring you into Luang Prabang, and the last ride is out to Kuang Si Falls.
In Vientiane you visit COPE, which supports mobility for landmine victims, and in Phonsavan the Quality of Life Association, which supports victims of unexploded ordnance.
From Luang Prabang you can keep going north: a village homestay, a day on the Nam Ou in a long boat, the border at Tay Trang, then the mountains to Sapa and the night train to Hanoi.