It will be a fun ride -- State Bike Route 9 is your best bet. It will take you from Albany and then up the western shore of Lake Champlain. You can take one of the ferries over to Vermont and Burlington.
You can email the state's program manager for the DOT's biking and pedestrian department - his name is Eric Ophardt and he can be reached at
eophardt@dot.state.ny.us -- ask for a copy of the State Bike Route 9 map. Great route map and it shows elevation, amenities, etc. Very handy.
You will, however, miss the worst of the mountains. There will be hills, but going from Albany to Burlington slides you up a gap between the Taconic mountains to your right and the Adirondacks to your left. The Hudson River Valley will hand you off to the Lake Champlain Valley.