Just depends on what you want to do. If you want a large pear tree of your choice, then topwork it. If you want no pears or smaller pear trees then cut and spray.
Remove the big ones and graft over the small ones.
Every year I dig up multiple dozens of Ash tree seedlings from my field, so I have similar issue but with Ash trees. I try to kill them while small with a tip of a spade or else once established, it’s tough job to uproot them.
You can cut them down but the roots are 4-5 feet long. You almost have to dig them up with a backhoe. I get rid of mine almost immediately before they get large. They have outlawed selling these trees in my state. They are a invasive and taking over all the vacant land around me. Get rid of them ASAP!!!
Round Up did nothing to them but make them mad. It did not kill the roots enough. They came back up the following year. It may work IF you really drench the ground with Round Up. Where mine are is around my pond area. I cannot , or feel right, using that much Round Up to try and get rid of them. They are EVERYWHERE in our state.