CAN bus termination in a fully modular design
The CAN bus is designed for a single line with nodes connected at intervals along it. In this standard layout it is quite obvious that you need to terminate each end of the line to prevent transmission line effects (reflections) at those ends.

In your layout this is not possible as there is no single line. Indeed, your layout will have some serious problems with reflections, not just at each unterminated end stub, but at junctions where multiple lines join. However, all is not lost. If the longest dimension of your bus is roughly 1/10 of the wavelength at the bitrate, then transmission line effects can be disregarded (basically the wave travelling time is much less than the bit time, so by the time you sample the signal value any transmission line effects will have died out). In this situation you can just bulk terminate the bus at the master node to ensure that the bus has sufficient load for the CAN drivers.

However, this means that the maximum bit rate you can run is limited by the length of your network, so you'll have to check this carefully. You might want to reduce the driver slew rate as well to clean up the edges of the signal, particularly if you are not running crystals in each node.

Edit: BTW Low-Speed and single wire CAN are designed for exactly this sort of flexible bus structure, so there is nothing inherently wrong with using CAN like this. The answer I provided above outlines how you can use standard CAN in this configuration as low speed CAN transceivers are harder to get now.