I have a 3/4" cold and a 1/2" hot water line going to a second floor shower. I was wanting to make the shower bigger and wanted to add another shower head and separate controls. Is it possible to get equal water pressure?

Rule of thumb, 1/2 will supply two fixtures, so if you are planning to have two separate shower valves with two shower heads, you should be just fine. However, if the 1/2" line also supplys a vanity, and the vanity is turned on at the same time as both shower heads, you may see a slight drop on hot pressure(volume). Most new single handle shower fuacets are temperature and pressure balancing valves, meaning they may drop in pressure, but the temp will stay the same. If its easy to run a new 3/4 hot line to the shower area and branch off to each shower faucet with 1/2, then I say do it, but if it's a major job, I think you will be just fine with 1/2 supplying both.