Just Like FAA
You'll find it's pretty much the same as the FAA medical. In fact 2 of the approved medical examiners I know in Lagos are also FAA, JAA and Canadian medical examiners. You'll have the usual BP, pulse etc. plus urine and blood samples. Audiogram. If you're over 50 you'll have an ECG every 6 months and if over 60 a stress ECG every 2 years. The eyesight is pretty standard, but you won't be allowed to wear your contacts for it. Take them along and tell them you normally wear contacts. You can do some of the test wearing your spectacles, including the reading card. You also have a color blindness test every medical and if you haven't done a medical here before you'll have to do a peripheral vision check.
I like Doc Frank Kupa at the Okupa medical centre. He's got a new modern clinic just for aircrew medicals at the back of his regular clinic. He's a pretty regular guy and very friendly and helpful. He does medicals for CHC and Bristow pilots, has a lot of family in USA and can keep your FAA medical in date for you.