The Syria opposition is not Al Qaeda. This is Assad propaganda.
To start off all the opposition were army deserters and local militias.
The West ignored their plight, so gradually the salafists had more influence. Largely are a result of the West's inaction.
Syria has a secular tradition so there has been considerable backlash against the salafists. Many times this has resulted in fighting FSA Vs salafists and Kurds Vs salafists.
Al Nusra was the main islamic fighting force but even they had a schism with the real fundamentalists leaving to join ISIS.
Including part time fighters and local militias there are probably around 150,000 armed people fighting against Assad. Of these something like 6 to 7 thousand are salafists. A smaller number of these are jihadists. A smaller number of these are Al Qaeda.
Yes, there is no doubt that some have been radicalised by the conflict. But the vast bulk of Syrians are secular and want a secular society. They will not tolerate sharia or a caliphate.
This is the easiest way to visualise the opposition:
https://pbs.twimg.com/media/BTbdKHVCUAEOwG0.jpg:large