North Cascades National Park is a mountain park with numerous alpine lakes. The Rainy Pass trail that goes to the top of Lake Ann is a good spot for sunset photos. You would need to hike one hour in the dark to get back to the trailhead though. I knew the Hidden Lake trail at east side was also picturesque although I did not get a chance to hike it because of leg injury. If I had enough time, I would do an overnight backpacking trip to camp on the top of Hidden Lake. The park is quite separated. The Artist Point at the end of highway 542 has stunning alpine scenes. Numerous photo opportunities can be found there. Please be sure to visit that area. Picture Lake is also a good sunset spot.
I also highly recommend the Skyline Divide trail, which is in national forest area outside of the park. The trail offers stunning view of Mount Baker as well as many other peaks. Sunset on the trail was amazing.
Sunset at Lake Ann
Sunset at Mapple Pass
Sunset at Lake Ann
Sunset view on Skyline Divide Trail
Mount Baker at Sunset | The photo was taken on Skyline Divide trail
Sunset at Picture Lake