Another reason you might want to stick with Air Canada (if they quit striking) is that you get better upgrade certificates for every 10000 miles flown (Elite members). On United, for every 10000 paid (Q?) miles they only send you 2000 miles of complimentary Upgrade Certificates valid for travel on UA within North America. For every 10000 Q miles, Air Canada gives you 4 any fare upgrades valid in North America from origin to destination (need 2 certificates for long haul and 1 certificate for short haul). If you do long distance travel (e.g. Calgary to Miami) then two certificates on Air Canada would get you all the way there (almost 3000 miles one way) whereas you wouldn't have enough with your 4 UA certificates to go one way. I like the origin to destination aspect of the Air Canada rather than the "miles" of United.