The other option would be YQR-DEN-EWR on the morning DEN flight. That gives you an ORD flight and a DEN flight later in the day as plans B and C, not to mention getting rerouted on Air Canada via YYC, YWG or YYZ and then connecting to United there.

I find it really difficult to get attractive Air Canada fares to US destinations ex-YQR or to YQR. When I do, the routes are stupid and while the milk runner in me doesn't mind picking up a bunch of extra miles, if my wife is joining me she absolutely will not tolerate it. (e.g. Air Canada suggested EWR-YVR-YYZ-YQR to come home last June, and United suggested the more wife-friendly EWR-DEN-YQR ) Of course, if you have eUpgrades to use up, flying UA can be a negative.

(Incidentally, UA offered us a $297 round-trip upgrade to United First on the DEN-SAN and SAN-DEN segments of our San Diego trip in February - and they offered it as soon as I paid for the Y trip. Very odd, and accepted in a heartbeat.)