Yes you can implement Modbus-RTU on the STM32F7 discovery board you have using the Max485; They both communicate using 3V signaling. The connections you will have to do is connecting RO to the Rx for USART6, DO to Tx of USART6 and both RE/ and DE to the same GPIO, choosing one available on the same Arduino connector, like PB4 (selected as TIM3_CH1 on the Arduino pinout, but you can change it to be a GPIO).
It is even possible that one of the Modbus master stacks available (like the one cited by JuliusCaesar) may support this chip or a compatible one. In all cases what you need is just a stack supporting the STM32 USARTs and using a GPIO to control the transceivers.
If you need to save as much power as possible, you will need to use two GPIOs to command RE/ and DE independently, disabling both the receiver and transmitter when the bus is inactive (this is possible as, being the master of the bus, you know when a slave can talk on the bus).