There’s a 7h or so RT over a generic return that saves even more I believe. Just had to be used within 7h or so which will fit your needs.

Remember at times there can be a bit of a wait for UPX so leave 45-60 mins to get back to YYZ once you arrive at Union. Also Union can be a maze if not familiar, especially with the continual construction.

Suggest leaving at least 60-90 mins for US CBP. I go for 90 without nexus and a NA passport. It can be busy at times.