In recent years, Peer-to-Peer (P2P) technology has been demonstrated tremendously effective in delivering large-scale video streaming services. Although P2P streaming is scalable and robust, the network-oblivious peering and scheduling in the current designs impede the further improvement in streaming quality and the efficient usage of network resources. New P2P streaming systems exploit network information provided by Internet Service Providers (ISPs) to achieve a higher level of application performance and generate lower traffic stress. In this paper, utilizing information from ISPs, we investigate the strategies on the topology construction and maintenance of multi-tree based P2P streaming systems. We study topology optimization to minimize the average height of sub-stream trees and the average propagation latency in each tree. We first present the optimization formulations, and then propose a set of heuristic algorithms for the construction and dynamic management of the multiple sub-stream trees for practical implementation. Through numerical comparison study, we show that our algorithms can significantly improve the delay performance of existing P2P streaming systems.