Just having a guest worker program will not suddenly start giving jobs to Mexicans and taking them away from American workers. It does nothing to make immigrants more qualified and takes away their low wage advantage. We've already seen that as unemployment has gone up, illegals have been going back to Mexico by the millions. Those who remain behind already have jobs or are part of the criminal underground. A guest worker program will make the working illegals visible and will expose those who are potential criminals. You would give the workers a work visa and round up everyone who doesn't have one and send them home.
The illegal immigration problem is one which comes primarily from the conflict between a natural free market in labor and government's attempts to limit that market and make it unfree. If you take away government's negative role in suppressing the access of workers to available jobs, then you have a healthier and more free labor market where workers go where the opportunities are and everyone benefits.
This is not to say that Workman's bill is perfect. It places an unreasonably high cost on a work visa at $4000. While he claims that's equivalent to what these workers pay a coyote to get here, he overlooks the fact that it will likely be in addition to those expenses which were already paid or will still have to be paid to get into the country if the federal government is not cooperating at the border.
Workman's bill includes some additional safeguards which may allay some concerns, but could be problematic. The guest worker permit would last for 8 years and applicants would have to pass a criminal background check. It also requires that employers provide guest workers the same benefits they offer other employees and that American workers be given preference in hiring. That last provision may be hard to enforce and along with the $4000 fee it might have a chilling effect and discourage workers from taking part in the program. For such a program to work it needs to be clearly advantageous for workers who are currently illegal to take advantage of it.
One thing which is clear is that Workman has done his homework. That 8 year duration is clearly based on studies which show that the average illegal worker stays in America for about 8 years before going back to Mexico voluntarily to enjoy the benefits of the money he has earned here. More than 80% of illegals do not want to stay in the US but want to return to Mexico and start their own businesses and thereby raise up the Mexican economy and create better jobs at higher wages there, ultimately reducing the pressure to come to America for work.