When you repack the bearings you don't remove the 'cup', just the half with the rollers in it. No force required. Clean the cups in situ & then check. If OK just re-grease in situ.
You might find this video useful in regard to what to expect to find. GQ & GU hubs are basically the same.
https://www.youtube.com/watch?v=Lt5jaIMhROE Video shows changing bearings, but if just repacking no driving out of the cups is required. If you do need to change bearings they should drive out with a drift fairly easily. Trick is to have things solidly on a couple of pieces to hardwood or similar to avoid 'bounce' when using the mallet. (Actually a club hammer with a couple of kilos in it is good - decisive blows, not wet lettuce taps) - bearing cup will come out with two or three blows if you move around the cup with each blow. I use a brass drift - less risk of damage to the bearing housing. Make sure the end of the drift is nice & square to avoid slipping off the edge of the cup. Something which would help the bloke in the video ....... once an old 'cup' has been removed it makes the perfect driver to put the new one in as he does (after lightly starting it with the hammer)..... but before doing that cut a slot through the wall of the old cup with an angle grinder. Works just the same but but makes removal once the new cup is fully home far easier, without risk of damaging the new cup in the process. If you have the disc laid on hardwood blocks either on a good solid bench, or a concrete floor, it will make the job easier over all, but also makes it easy to know when the new cup is fully home. You'll hear the tone change when knocking it in & it is as far as it will go.
I made my own special tool to remove the bearing retainer. But after a couple of uses bought the proper thing - much better & cheap. eg.
https://www.ebay.com.au/itm/Hub-Adju...QAAOSwqr5duusm
The two little screws which hold the bearing retainer from unscrewing don't need overtightening, but I always use a bit of blue loctite threadlocker on them just to be sure.
A helper with clean hands to take photos at each stage of removal is handy, so you don't get your phone/camera covered in grease. Have plenty of rags handy & I like to wear some of those rubber gloves that supercheap, repco & the likes sell.