Usually, third-party f/6.3 zooms still autofocus on Canon bodies because many of them report themselves to the camera as f/5.6, keeping AF enabled. Since f/6.3 is only slightly slower than f/5.6, autofocus often works reasonably well in practice.

The bigger limitation is with combinations that truly report slower than f/5.6, such as some lens + teleconverter setups that become f/8. On the 1D X, Canon disables AF once the reported maximum aperture is smaller than f/5.6, so those combinations are the real concern.

So: for the Sigma/Tamron f/6.3 lenses you listed, AF will generally still work if the lens reports f/5.6. For Canon lenses or teleconverter combinations that honestly report f/8, AF is not supported.

This matters most to some wildlife shooters using long lenses plus teleconverters, especially compared with earlier 1-series bodies. For most buyers, it is a niche issue rather than a general problem.