Yesterday was not an easy one for UA staff given weather issues along the NE coast and operational ripples through the system. I was able to move my Monday AM flight to ORD via EWR to a nonstop to ORD last night so I will still catch my HKG/SIN flight later today. When I got a text advising my YYZ-EWR morning flight was cancelled I checked and saw open seats on yesterday evenings two flights to ORD. As a 1K I could make a same day change without charge, but could not get through on the phone, nor do a change online, so decided to finish packing and head for the airport. Suffice to say I was able to get through to an agent who got me on the 5:25p flight and confirm my upgrade. By the time I got my boarding pass(es) from the kiosk, the first of several delay notices arrived by email and text. After three gate changes and about 3-hours, we boarded our 737-700 (12 F seats). When investigating flights earlier in the day, I saw there were two open F seats on this flight (actually C since trans border flights call it business) and the other 10 passengers had all checked in. There was also about 8 elites on the upgrade waitlist. I jumped the queue leaving one open seat. However, by the time boarding was completed, there were three open seats in F, 1B and the two across the aisle from my 2B. Knowing there had been eight elites waiting I was wondering why the gate agent didn't go into the economy cabin to move three people up. I've had this happen before ex-YYZ, in one case being a 1K sitting in E+ and seeing an empty seat as we pulled away from the gate. I realize with the delays, like missed connections, gate changes and other matters, it wasn't an easy day for the UA gate staff, but should not the agent have moved three elites into F?