I second the Rt 100 suggestion. It's a great ride starting at the Canadian border and heading toward MA. Vermonters are quite cordial in their driving habits toward cyclists. The out-of-staters can be more aggressive. Generally, you find more traffic the further south you ride. Most of the bike touring companies conclude their Vermont routes around October 15. This indicates to me that their years of experience shows that seeing good foliage beyond this time is less likely. I've done 7-8 Vermont autumn tours and I find that the last week of September or the first week of October is usually the peak foliage time. If you like to climb - even with touring gear, there are some wonderful climbs to be had off of Rt 100. They are affectionately known as the "Gap" rides for the 4 or so mountain gaps (passes for those in the western US) you get to climb over. Here is a link you could check out for directions on the Gap rides and other northeastern rides.
http://www.northeastcycling.com/
I have yet to cycle in Vermont any meaningful distance without having to walk, uphill or (out of fear) downhill. Lincoln Notch in the center; Smugglers notch in the north; sometimes rt 9 up from Brattleboro out of shear exhaustion from the lengthy grades.
You may see signs at the top of these notches:
Attention: Check brakes for porcupine damage. What happens in the early spring and summer is the mud is still salty from the winter, gets onto the automobile undercarriage, and then the porkys chew it for the salty taste and flavor. You discover at the top of a mountain you have no brakes. Never had this problem with my bicycle.
roughstuff