What button do you have to use and what do you think it should be to get into cover.

it will most likely be the action button. the one you use to talk to your squad mates or from eib the one where you can steal ammo from your squad mates. its very context sensitive just like the command ring

oh, by the way, welcome the ubi forums, consider it a massive waiting room for all teh hells highway fans, pick a number and have a seat!