Route: MapMyRide — Strava. Nicely described by Rawlins at BestRides.
Traffic: Two distinct sections:
The first section is between Sunol Glen Elementary School (starting point) and Geary Road (5-mile mark), which leads you to Sunol Regional Wilderness, a fairly popular destination in spring. In this section, there was mild traffic in the morning. By noon, traffic had increased quite a bit. I would call it moderate.
The second section is between Geary Road (5-mile mark) and Felter Road (15-mile mark). This section had hardly any traffic. We saw about one car every fifteen minutes in March 2015.
Climbing: Gentle climbing throughout. Only one steep section: "The Wall", which constitutes the last 0.2 miles along Calaveras Road before it meets Felter Road. The words "The Wall" were painted on the road.
Bike Trails: None, but there was a comfortable bike lane throughout.
Views: During the first five miles (upto Geary Road), we see hills on one side (Sunol) and large flat landscape on the other side.
Beyond Geary Road, Calaveras Road is shaded and climbs about 500 ft. At around the 9-mile mark, Calaveras Reservoir starts coming into view. This is the best part of the ride. Lush green hills and blue waters of the lake make for gorgeous views.
Finally, at the intersection with Felter Road, we saw a large meadow with horses. Before this location, there were no farms or residential complexes. Near the intersection with Felter Rd, traffic suddenly increased; we saw many homes.
Water stops and restrooms? None. Near Geary Road (5-mile mark), the route was quite forested, so it was possible to take a quick restroom break in the woods.
Extensions: (a) Include Piedmont Rd and Sierra Rd, (b) include Felter Rd, (c) Best of the Bay Century, (d) any route from Fremont BART? For example, see MapMyRide. Each of these routes includes riding along city roads, so it is not as 'pristine and pure' as Calaveras Road.