Minimum Wage effects on Adjacent Cities When a city like Seattle raises the minimum wage to 15/hr, how does it affect the labor market in adjacent cities? 

Are there examples, studies or accepted practices to address: Difficulty staffing entry level positions when labor pool can work across the street for several dollars/hr more?
A very famous study in this direction is Card and Krueger (1994).
They look an increase in the minimum wage in New Jersey in 1992. While New Jersey raised the minimum wage from USD 4.25/h to USD 5.05/h, the minimum wages remained at $4.25 in adjacent Pennsylvania.

You should have a look at the subsequent research.