If you're doing animation to be video, or that only has to play in an Android or iOS app, or that only has to play on a desktop browser, you should use an ActionScript 3.0 FLA, and then you can use Stream as the sync. Also, make sure to use WAV sounds and not MP3, that will give you much better scrubbing.
If you have to use HTML5 Canvas, which only makes sense if the animation has to be viewed in a mobile browser, then you can only choose Event as the sync, and you either have to write code to make the animation skip frames on slower devices, or you need to make your animation simpler so that it can keep up with the sound. Also, make sure to use MP3 and not WAV, because WAV sounds can sometimes be distorted when used inside an HTML5 FLA.