Plan Mt Stuart over the weekend, then Shuksan and Baker. Blue bags encouraged? required?

Blue bags for sure on Baker and Shuksan. Stuart not so. Sounds like a killer trip. Good luck and have fun.

I thought it might be all 3 with high use. BTW, doing all 3 (hopefully, weather permitting) in a week not a weekend.

Depends on what route on Stuart and where you bivi. If you are doing Cascadian Couloior and bivi by Ingalls creek you can dig a cat hole. If you are doing West Ridge and bivi on the route bring a blue bag. North side route you will camp in the moraine, but the forest is close by and you can probably dig a cat hole if there is not too much snow.