Standard humbucker designs with a single bar magnet underneath the coils and steel slugs/screws generally have less magnetic pull than a rod magnet single coil for the same magnet type.

From someone's reply to a magnetic pull question on another forum: "Using a Gauss meter to check strength at the pole, most A(lnico) 5 rods usually read 800 to 1200 gauss. A(lnico)3 will usually read 500 to 700. Humbuckers don't read so high at the poles. They usually read anywhere from 200 to 500 at the poles, though a thick ceramic type pickup like a super distortion can read 500 to 700 at the top of the poles".

Ceramic magnets underneath steel pole pieces in a single coil (like the standard kit single coil pickups have), will have the field weakened by the steel pole pieces, but ceramic magnets are more powerful than Alnico 5, so you generally end up with slightly more field strength than with rod magnets.

So like most things 'it depends'. But given the same magnet type in all the pickups, and the pickups set the same distance away from the strings, single coils will have a greater magnetic field strength than humbuckers, and so will affect the strings more.

So, one humbucker is probably equivalent to one single coil in terms of pull, but the amount of pull is very dependent on the magnet type used.