I have Mercury in Cancer and I am super emotional. But I also have my Moon in the 1st House so that probably adds to it a lot. Can't say for Cancer Mars people. I think Mars only comes out when you are trying to assert yourself, do something physical or whatever... I have Leo Mars and I am not bossy or very Leo-like, but lord, don't put me in a competition because I won't eat or sleep and I'll work overnight while everyone is asleep just to win.