I was on paid business flying from BRU to YUL last week, waited ~1hr at customs/immigration in BRU (arriving from Entebe) . Then again ~1 hr at Canada customs connection area. Both certainly felt dysfunctional. I would have just gone through Nexus and back through security but had some Belgian beer in my carry-on for a friend.
I think Skyteam (Air France in particular from my experience) takes better care through immigration/customs and really makes for a better experience