Designing a CANbus+DC power network of sensors
What do you think about this scheme?


From the OP it seems you describe mixed topology with very long runs. The CAN bus is not particularly suitable for this. It is designed for single long run with multiple very short stubs, i.e. the opposite of what you propose. You might be able to make it work but only at the extremely low speed.

My recommendation would be to use CAN bus repeaters in place of those "UTP splitters" in the picture. You can use commercial modules, like this one or make your own based on any MCU with built-in dual CAN controllers. Note, that 75m long runs will still be a limiting factor in the maximum speed you can get from this. 1 Mbps is definitely out of question.


  I know that CANbus is very immune against noise and the length are not
  near the limits, but it can bring me trouble having so many
  connectors?


Connectors should not be a problem if you design your boards properly. Texas Instruments has many papers with recommendations that you should follow, like this one or this.

Correct termination is the key. CAT5/CAT6 cables you are planning to use have 100 Ohm impedance, which is different from 120 Ohm CAN specs. You need to match this with 100 Ohm termination resistors and then make sure 50 Ohm total is within the acceptable load parameter of your transceivers. Here is useful TI forum topic on this subject.

Another thing to consider is using isolated transceivers and dedicate 1 or 2 conductors for "CAN ground", instead of using negative power line for it. This is because 75m cabling in outdoor environment might result in common mode voltage going beyond CAN specification.


  What about the DC power distribution? considering that the whole
  system will be powered by a battery placed near the main board (I will
  make intense use of the low-power modes of the MCUs). What about the
  power losses?


The right way to deal with power losses is to increase bus voltage and use DC-DC POL modules on your data acquisition boards.

In our modular wheelchair electronics we are using CAT5 cables and dual RJ45 connectors on each board. 4 out of 8 conductors carry 24V power and each board has tiny 24-to-3.3V DC-DC converter, powering MCU and all attached sensors. All boards are daisy-chained and extra jacks at the two ends have plugs with terminating resistors.

Note, that we did not use all available conductors for power. Instead, we have "enable" signal line that controls those DC-DC converters. This allows us to effectively power down entire network by the command from master node, further increasing power savings.