Thanks everyone for your thoughts.

Firstly, I will be applying for Nexus asap (last time I flew out of YYZ, the customs line took approximately 1 hour) given the incredible time savings.

Secondly, I agree with the comments about the UDU (I have about 75-85% success rate out of Chicago) and expect it to be pretty good out of Toronto. While it is not real "first class", it beats having to sit in back in an RJ especially given I don't like to check bags.

Lastly, it looks like redeeming on AC metal has a very high YQ fuel surcharge. Staying with UA allows me to avoid that and also gives me good options for redemption out of Buffalo (not too far from Oakville where I plan to reside).

Again, many thanks to all of you.