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