I've never seen the transfer line having NEXUS only scanning, but there is a NEXUS/priority line to jump ahead if they are at all busy.
I think there are only two AC flights daily, but there are re-connection options with UA through Chicago. I don't know if a non-status, non-IROPs misconnect would entitle rebooking on another airline, though. Probs no.
Again, it depends on how tight the meeting in MSP is. If the next flight out of YYZ still gets one there in time, ¯\_(ツ)_/¯