OP, your question is about the YYZ end or the ROC return? If you are flying a UA aircraft on a AC codeshare, your ticket likely says check in with UA. That is in the same terminal at YYZ as AC, but separate. I don't know what you mean by blue and red BP.

kwflyer, ROC on the beach? Did I miss a beach flying out of Rochester for 3 years?
It is a small airport though. (I lived there before 9/11 so enjoyed basically all-Rapidair type of deal. Leave home an hour before the flight, get met at the gate etc.) Navigating through the airport is easy.

OP are you familiar with the Star Alliance Lounge Finder? There is also *A app that will identify lounges if they exist. There are none listed at ROC. Same deal at BWI, MSY, even MCO (though there is now a PP lounge). Not really AC turf and they leave us hanging.

Edited to add, seriously, it is faster to drive there. 3 1/2 hours by QEW. One time I was scheduled to fly there to speak, but there was airline strike and I drove. Allowing the travel to YYZ and arriving the required advance time before flight, the minimal flight duration, and drive to the local destination was almost the same.