My update on the FRA - YUL - YVR connection as promised.

Bottom line: piece of cake. We landed exactly on time, which gave us one hour and forty minutes until our next flight. We ended up having 25 minutes to spare in the MLL before boarding began. Immigration moves fast with the automated machines, bags come out quickly, priority delivery is observed, and the connections counter is just past immigration. There was nobody at security either (but we had our nexus cards at the ready had there been a line). As long as your inbound is on time, you should be fine.