Title says it all. Is 1h 55m enough of a layover in Munich for a Montreal > Munich > Athens flight?
We are both Canadian citizens.
You mentioned in the comments that your airline would be Lufthansa for both flights. This means, you would arrive at and depart from terminal 2 in Munich (or its satellite). Terminal 2 is just a very long corridor with gates at one side. Google Maps estimates it to be 900 metres long (about half a mile). You can clear the entire terminal from one end to the other in about 15 minutes, 20 if you walk slowly.
Either of your flights may depart or arrive from the satellite terminal (if I had to choose one I would choose the Athens one based on it probably being a smaller plane). To get from the main corridor of terminal 2 to the satellite you need to take an underground shuttle train; the platform to this is bang in the middle of the corridor. The travel time from one end to the other is 60 seconds, according to a forum post I just found. The satellite terminal is not as large as the main terminal so you can probably reach the outermost extreme in about 5 minutes.
Finally, when arriving from outside Schengen (e.g. Canada) and transferring to a flight within the Schengen Zone (the one to Athens) you need to pass both immigration and a security screening (although Canada may be considered ‘clean’, i.e. not requiring security re-screening; I’m not sure). As far as I know, these are conducted in the main terminal although I don’t remember whether there is more than one controlling area; there definitely is one bang in the middle of the hallway approximately across from the entrance to the shuttle. Passport inspection and security screening will obviously take some time but shouldn’t take forever. Let’s assume 20 minutes and you’re probably super-covered.
All in all that means without having to rush you can make connections as short as 40 minutes even if your two flights’ gates are as far apart as possible. So the two hour transit is definitely doable.
If your airline from Canada to Germany should happen to be Air Canada, the same still applies because Air Canada is also a member of the Star Alliance (terminal 2 is for exclusive use of Lufthansa and its Star Alliance partners).
What would be the best way to find this (whether you are on one PNR or not) out prior to purchasing the tickets?
It has been mentioned in the comments that if your flights are on a single booking (i.e. with a single PNR or booking code), then the airline believes you can make the connection and it becomes their mistake if you don’t (as they were confident enough to sell you the entire trip; they entered a contractual obligation). Thus, the fool-proof way to find out is by checking the airline itself.
Sites such as Google Flights will generally hide connections that are booked on separate tickets so when checking Google Flights without changing settings everything you find should be safe. If I recall correctly, SkyScanner shows multi-ticket itineraries but adds a red flag saying it’s your own risk; there is most certainly an option to hide it, too.
What I always do after comparing prices at Google Flights, SkyScanner or others is to go to the airline that was mentioned and perform the same search. If the same itinerary shows up then you are absolutely safe because airlines will not offer multi-ticket connections as far as I am aware (meaning you will need to either do multiple searches or mess with well-hidden options).
Assuming you search for a connection between Montreal and Athens (and do not try to put together separate flights yourself), what you are offered should be on the same booking/ticket, unless explicitly stated otherwise.
With the entire journey on a single booking, you should have plenty of time if your first flight is not very late. You will have to clear passport control (immigration) in Munich and you may have to go through security. Your bags should be sent directly to Athens, not being available to you in Munich.