For rooting, look up CF-auto root or kingo root, CF-auto uses odin pc so you may want to read up on that, I use version 3.07, others have used 3.09. For rom choices, you want to make sure you are selecting a rom for i337m, there are also roms for i337 which is the at&t version, if it doesn't specify Canada or i337m I would stay away from it. There are ASOP (sort of a vanila rom) and touch wiz roms suggest you read up on the differences. To flash any rom you need a custom recovery, I use TWRP version 2.6 some say to use 2.5 and I would suggest staying away from the latest and greatest since I have seen a lot of issues using the newest versions. Some people use Philz recovery which I am not familiar with but have seen quite a few successes with it. The last option is clockwork recovery, though I have used it in the past it can be finicky and I have seen people have a few issues with it. Lastly unlocking, if you going to unlock, I would skip all the free methods and use a reputable service like unlocker.com or something like that.... again read up before hand.
Best advice I can give, if your going to try something, read a lot make sure you know what your doing and be paitent, some processes look like they are doing nothing but allow them to finish.....