All the hikes I've ever been on have been on the west side of the Cascades.
I just found a trail though listed at 38 miles one way, that takes 5-9 days to hike.
This is the Chelan-Summit Trail, and it's listed as being hikable from early July through September.
Green Trails Map No. 115 Prince Creek; Green Trails Map # 83 Buttermilk Butte; Green Trails Map # 82 Stehekin
Regarding this trail, because of the distance covered, it's suggested that you call the Chelan Ranger District to make sure that the trail is in repair and
completely hikable.

