Canada - International Transit thru YUL

I usually transit through YYZ but have a flight next week from FCO thru YUL and on to YVR.

My question is whether or not I will have to clear customs and exit the secure side like you have to do in YYZ?

I find it a real PITA when I have bought duty free and have to carefully pack it into my checked bag before going back through security and on to my connecting flight.

Well, if you're going FCO-YUL-YVR, then you're in fact not transiting internationally, but to a domestic flight.

In this case, yes you will have to clear Canadian immigration, claim your bag, clear customs and then go back "in" through security to your domestic flight.

I usually transit through YYZ but have a flight next week from FCO thru YUL and on to YVR.

My question is whether or not I will have to clear customs and exit the secure side like you have to do in YYZ?

I find it a real PITA when I have bought duty free and have to carefully pack it into my checked bag before going back through security and on to my connecting flight.

Yes - you always (no matter what airports, airlines, or countries) clear customs and immigration formalities at your first point of entry into Canada.