Normally the due IO pins only can stand 3.3 V, but what about the I2C? Can i use the bus with 5V? i cannot find a good documentation about the I2c specification for the due.
The I2C bus itself is voltage agnostic.
It depends on the specific I2C devices you pick and use. Some will work like the TI ADS1110 I2C ADC chip from 2.7V to 5.5V, other I2C chips may not work at over 3.3vdc. Some like the popular RTC DS1307 is a 5 volt only device.
Lefty