Hi,
Below will be some comments on regards of your questions:
1. what is the maximum bandwidth of the ETH2CAN channel?
For the information available, there is no specific information on regards of the bandwidth itself. There is though a test setup that was done with the following setting:
CAN Baud Rate: Arbitration = 1Mbps, Data = 4Mbps
PFE: 1Gbps RGMII
2. How to handle ETH2CAN and CAN2ETH concurrency, this two scenario will both use 8M SRAM for data exchange, is here strategy for the resource manage of SRAM to avoid data flow conflict.
We understand that there are specific buffers which manage the CAN2ETH and ETH2CAN bridge. An example is shown below:

Please, let us know.