CorelDraw supports import of documents from Microsoft Publisher (.pub) and can open them, so there is nothing more easier than to save them as default CorelDraw's cdr graphics file format.
Some users report that the import process is not 100% perfect, but of reasonable quality. As far as we know, there is really no other alternatives to CorelDraw for pub to cdr conversion. Maybe it's possible to save from Publisher or convert pub files to other format like PDF and then import it to Corel.
Updated: January 11, 2017