3 Days on Lake Maggiore

Stresa
Borromee islands (isola Bella, Isola Superiore or dei Pescatori, Isola Madre)
Lake Orta
Orta San Giulio (village on lake Orta)
Cannobio
Locarno (Switzerland)
Cento Valli scenic railway from Locarno to Domodossola.

Roberto's suggestions, as always, are excellent, just don't try to cover all of them in just 3 days! If you are interested in amazing, elaborate gardens with a few white peacocks thrown in, just to guarantee the "over the top" factor, be sure to visit the gardens on Isola Bella. The villa bottom floor is especially interesting & unique. Then go to Isola dei Pescatori to unwind & relax & maybe even do a bit of swimming. All of the above will take up at least half a day, probably more, and could take up a whole day if you prefer to really take the time to explore.

Roberto always has some good suggestions. I'll be in Lake Maggiore for several days in September. I was planning on that railway trip Roberto put. Also i'll add one thing, is I like hiking the outdoors and was planning on doing a hike in the morning and afternoon. I picked up this Cicerone Book for walking/trekking around the lakes and the trails. Just started reading it and still narrowing down which 2 hikes I'd do. It also covers Lake Como and Garda.

http://www.cicerone.co.uk/product/detail.cfm/book/824/title/walking-the-italian-lakes#.Vp-MErerSUk

Robertos suggestions are spot on. Please take the boat over and eat lunch at Verbano on Isola Pescatori. I have stayed in Stresa, Baveno and CAnnobio on this lake. Cannnobio is, by far, my favorite town.

We stayed at the hotel Verbano on the Isle de Pescatore and loved it. There was a nice terrace that looks over the lake and mountains and was a great spot to rest on jet lag afternoon. They have a decent restaurant and we got half board when we stayed here.