I am using OpenCV to capture video streams from two USB webcams (Microsoft LifeCam Studio) in Ubuntu 14.04. I am using very simple VideoCapture code (source here) and am trying
It is not possible to stereo sync two common webcams because webcams lack external trigger feature that lets one precisely sync multiple cams using a common trigger signal. Such trigger may be done both in SW or HW but the latter will give better precision. Webcams only support "free-running" mode and let you stream whatever FPS they support but you can not influence when exactly the frame integration/exposure is done.
There are USB cameras with a dedicated external trigger feature (usually scientific cameras like Point Grey) - they are more expensive (starting at about $300/piece) than webcams but can be synced. If you really are on low budget you can try to hack the PS3 Eye camera to get the ext. trigger feature.