I went from Garmisch to Riva last year. It was fun. If you want I'll check for my GPS record. Munich would be one more day...  The Via Claudia is a standard route - some guys call it "smooth"...

Just check for "Heckmayr Route" or "Albrecht Route"... 

Another website worth checking is: www.gpsies.com.

For return we used one of the shuttle services that are available at the Lago di Garda...

Consider staying a few days at that lake. The trails are incredible!

I've been there several times for racing - and vacation...

Bernhard