Ambassador Rodley said corruption has costs the Cambodian government an estimated $500 million a year.
Cambodia marked the 10th anniversary of the International Year of Volunteers last week, as officials called on more volunteers.
Yingluck, who was elected in July, is scheduled to arrive on Thursday, with Thaksin preparing for a weeklong trip starting Friday.
Thaksin is expected to give a lecture on Asian economics on Saturday and to play a round of golf with Hun Sen in Siem Reap on Sunday.
Aside from promoting trade, the business association also seeks to promote Cambodian culture.
A weak recovery to the global economic crisis in 2008 has not helped.
Cambodia's civil servants have long relied on facilitation fees, because their salaries are typically around $50 a month.
A group of young engineers say they are ready for the government to make use of their skills but are facing limited job prospects.
Cambodia exports labor to Japan, Malaysia, South Korea and Thailand especially.
In the past decade, new roads and high-rise buildings have changed the landscape of Phnom Penh.
The plan calls for an “economic corridor” linking the Greater Mekong countries and investment in urban and rural areas alike.
While welcoming the launch, economists warn that mismanagement of the bourse could also lead to economic woes.