I've seen a number of threads in this forum about a lounge Air Canada passengers can access at FCO (Leonardo da Vinci–Fiumicino Airport in Rome). It seems like the situation has fluctuated quite a lot lately, but here's the situation as of June, 2017.
There is no Maple Leaf Lounge in Rome. Neither is there a Star Alliance lounge. However, Air Canada has worked out a deal with Alitalia to use their lounge in Terminal 3, by the E gates. So after you pass the very bored passport control officers, proceed through the inevitable duty free area, and to the very end of the corridor. As you reach the end (it's not very long) you'll see an Alitalia help desk and then the terminal branching off to the left and right. Take the left fork, and you should begin to see signs to the lounges. An escalator leads to the British Airways and Alitalia lounges. Head into the Alitalia lounge and present your Altitude card (since, at least in my case, it wasn't enough to just show a boarding pass, even though it had my status printed on it). And that's it.
The lounge isn't the nicest in the world, nor the biggest, but it's pleasant enough and has reasonable food choices--mostly pastries and the like. There was also a tray with scrambled egg, sausage, and potato. The downstairs is beautifully air conditioned (the best AC I've had since landing in Rome) while the upstairs, which is quite a lot smaller, is almost unbearable. They announce boarding for AC flights, which is helpful.
(It is possible there is a second lounge available to AC passengers, but once I found this one I just settled in.)
This thread has been superseded my a master thread with a directory of all AC contract lounges. Please visit that thread for information on FCO lounge access. Adam Smith, AC Forum Moderator