Problem Solved !
I did'nt really found why it was not working on my first prototype but I faced the same issue with my final PCB.
However there was a short circuit between the CAN TX and RX on one MCU due to a thin wire of tin !
Even with that problem i had the RX signal on my scope that's why i did'nt thought it was a hard problem !
I removed the bad ...
I was wondering whether there's any problem in using the divider instead of step-down regulator.
A step-down regulator (Switching regulator) is better or required when the Power Dissipation using a voltage divider circuit or a Linear Voltage Regulator, is too high.
For example when you are powering a device from a much higher voltage source. With a 20V ...
The best option, when possible, especially in the case where there is a single I2C master, is to pull up to the same VCC as the I2C master. In your application that would be the Raspberry Pi VCC, I guess.
But it is still an interesting question. The basic answer is, yes, you can use a divider for pullup.
The effective pullup voltage is V * R2 / (R1+R2) ...