Depends where you’re staying and wether on or off road. No idea about off road, but we rented a little apartment in Limonta, just round from Bellagio, a few years ago so I took my road bike out for some cheeky early morning rides. Absolutely fantastic place.
You’re probably looking for off road, but if on road just go to mapmyride or something and put some routes together, then download to GPS. Or buy a half decent map 🙂
If on road you can take your bike over on the ferries too and ride one leg of the lake at a time. Ride up to Madonna del Ghisallo, there’s a cycling museum up there and a church to the Madonna who is apparently the patron saint of cyclists. Some fantastic old bikes in the church as well as the museum. The Giro goes up the climb from Bellagio and it’s fricking tough, but you can go the (long) back way to the museum and then descend if you don’t fancy coughing up a lung in 30 degree heat.
Edit: If you’re road riding obviously early is best to avoid the heat, but the main lakeside roads get pretty busy with commuters and wotnot. They’re very cyclist friendly but the roads are narrow and winding, and the italian drivers are…. italian so best avoid ‘rush hour’