I wonder if this sample return Mars mission will also be the maiden flight of the Long March 10 rocket?
Using CZ-10 is a possibility, or even the preferred option. But certainly not the maiden flight in 2027. It is the wrong time, also too risky for a launch window of 2 weeks in 2 years, no room for mistake. I would expect CZ-10 in its maiden flight to put a big lander on the moon as part of the moon base program, then go to Mars in 2028 after examing the performance of maiden flight. There is still room to fix any problems or switch to combo of CZ-3 and CZ-5 which is the other option..
If development of heavy rocket (CZ-10) is at risk, it can be considered to use existing rockets for two launches (CZ-3 and CZ-5).