On the contrary. We have had an ongoing guest worker program for quite some time: the H2A visa. And it has precisely the effect I pointed out, which is, that it actually encourages more illegal immigration in the form of family members crossing illegally to join up with the H2A visa holder wherever they might be.
The implication of your post is that illegal immigration occurs because of a labor shortage in the agricultural labor market, and that if we had a program that legalized such traffic, then the situation would stabilize. This is simply not true, and it has been amply demonstrated that illegal immigration occurs because of the difference in living standards and the availability of taxpayer funded social welfare in this country. Were we to expand the H2A program and rechristen it "Bracero II", with no quota, the numbers of people still trying to cross into the U.S. would vastly outnumber the available Ag jobs.
Illegal immigration from Mexico occurs because of the massive increase in the Mexican population since 1960, the utter and abject failure of Mexico's political and social "institutions", and the rise of court mandated participation of illegal aliens in the social welfare benefits of the United States. No guest worker program will ever solve those core realities.
There have been several studies done, including by the CIS that suggest we could reduce labor demands in agriculture dramatically through increased mechanization, which is no secret to anyone.
As long as an endless supply of cheap and compliant workers are handed to farmers on a silver platter there will never be an incentive to modernize. And the illegals will never stop coming, guest worker programs or not.