Your other post says "starting is Stresa and ending in Milan.", here you say "Then back to Stresa for a night.".
Southern Switzerland has a lot of mountains (obvious), but this means that there are a limited number of roads going across these mountains, but these pass roads are spectacular
When are you going? Summer I hope, as many passes over the Alps are closed by snow from November to May.
I would suggest, from Stresa the route north goes over the Simplon pass (you need to follow this route on a map), and down to Brig.
Turn right, to carry on up the Rhone valley (the river that enters the Mediterranean near Marseille). Then at the end of the valley (Rhone Glacier in front of you) turn left, and over the Grimsel Pass.
I suggest you go to YouTube, and do a search for "Grimselpass" and you will see what I am talking about.
This takes you into the Aare valley, you are now on the north side of the Alps, the Aaare is a tributary of the Rhine, which ends up in the North Sea at Rotterdam.
Keep going down the valley (there is only one road), past Meiringen - stop to visit the Aaareschlucht (gorge), on to Interlaken. Stay in either Grindelwald or Lauterbrunnen (both are car accessible) for 4 nights.
Then on to Luzern for 2 nights.
From Luzern you take the Autobahn back to Italy. Long tunnels including the longest one under the Gotthard pass. You don't see as much, but it is a faster return route.