Check out the following link and follow the instructions if you haven't already: http://www.cic.gc.ca/english/information/medical/medexams-temp.asp
If you haven't received instructions and a personalized form directly from CIC then you will be going for an up-front medical which is totally fine. You don't need to bring any forms, just your passport and prescription eyewear. If you have prior medical conditions that aren't obvious then you will want to bring a letter from your family doctor describing these.
Also, check with the clinic ahead of time to see if you have to bring photographs or if they will take your photo there. And it's a good idea to check on their methods of payment as you may have to bring cash.
Other than that it is just a couple of hours spent with a doctor and lab techs. Have fun!