I generally find that the smaller the bun, the more they squirm around and struggle when being held. They are generally easier to pick up but harder to hold on to. The larger ones I've dealt with are for some reason just better with being handled. But there is once in a while a large bunny who does not want to be held -- and those are hard to pick up AND hard to keep a hold on. I have definitely met bunnies who don't care! You can pick them up, you can hold on to them for a couple of hours, you can do what you want and they'll just go with it.
I have 2 medium buns and one dwarf mix bun. They pretty much know they won't be eaten or harmed when picked up by now (had them about 2 yrs). But it is a matter of their mood and how much time they let me get away with. I know this because when they are in situations that truly are scary to them (vet's office, strangers nearby, or in a different environment) they jump into my arms and cling on for dear life.
It's tough to "train" them into being better at handling but the two things that are in your control are doing it often and doing it right. If you hold them in a way that makes them feel secure, over time they will know it's alright. If you do it often and each time it ends badly (i.e. they fly out of your arms, they struggle and twist around furiously, you yell or scream out of nervousness/fear) then they are going to fight you harder each time you try. It's tough to get good at holding a bun, though practice makes things better. Having strong, firm arms helps, and holding them close to your body for support makes them feel grounded and safe. Pick up and put down the bun quickly and decisively. After repeated good experiences with being held, my buns learned that it wasn't the end of the world. I don't pick em unless I have a need to (grooming, nails, health check, etc.) so they have learned to put up with it and the sooner I finish the sooner they get let go. And there is, of course, always a celebratory treat at the end of the ordeal
Even if they have to flick me off and thump at me afterwards!