Two major factors that limit the throughput in multi-hop wireless networks are the co-channel interference and unreliability of wireless transmissions. Multi-radio multi-channel technology and opportunistic routing (OR) have shown their promise to significantly improve the network capacity by combating these two limits. It raises an interesting problem on the tradeoff between multiplexing and spatial diversity when integrating these two techniques for throughput optimization. It is unknown what the capacity of the network could be when nodes have multiple radios and OR capability. In this paper, we present our study on optimizing an end-to-end throughput of the multi-radio multi-channel network when OR is available. First, we formulate the end-to-end throughput bound as a linear programming (LP) problem which jointly solves the radio-channel assignment, transmission scheduling, and forwarding candidate selection. Second, we propose an LP approach and a heuristic algorithm to find a feasible scheduling of opportunistic forwarding priorities to achieve the capacity. Simulations show that the heuristic algorithm achieves desirable performance under various number of forwarding candidates. Leveraging our analytical model, we find that 1) OR can achieve better performance than traditional routing (TR) under different radio/channel configurations, however, in particular scenario (e.g. bottleneck links exist between the sender and relays), TR is preferable; 2) OR can achieve comparable or better performance than TR by using less radio resource.