Federation of Cloud services is notably landing interests from both Cloud providers and consumers. Cloud providers nowadays are required to form federations to remain competitive, and sustain their market share. Cloud consumers however seek optimized services from Clouds federation. They strive to maximize their satisfaction level, which is often measured by Quality of Service (QoS). Federations are governed by a mutual contract known as Service Level Agreement (SLA), which both consumers and providers must negotiate, so as to reach an agreement. The focus of this paper is to address issues related to SLA negotiation for the purpose of QoS assurance within federation of Clouds. We define, and specify an automated SLA negotiation model based on Fair Division Game. We evaluate our model using different use cases, and the obtained results proved fairness, and efficiency of the proposed SLA negotiation model in CloudLend.