a formalized guest worker program will simply allow businesses that would not normally hire illegals - to now be able to do so legally. Home Depot and Walmart and alot of other low skill service businesses will be loading up these guest workers, and lowering wages. the businesses that hire illegals now, paying cash and paying no taxes - will simply continue to do so.
Not if the proper "carrot and stick" policies are enacted. If it is easer (cheaper) to hire a legal worker than risk the fines of hiring an illegal worker, or of a worker being here illegally, then only legal workers will be hired.
No "guest worker" program has a prayer of working unless it is combined with some "stick" component that will make that balance work.