How much flying do you expect to do (both segments and miles) in each of 2010 and 2011 on each AC and UA? Will it even be enough to gain status on either? What kinds of fares are you planning on purchasing? Will you be flying mostly with the US, within Canada, transborder, or international?
If you will fly Tango on AC then you don't have to worry about gaining status on either AC or UA. Please provide more information so that we can advise you better.
BTW, welcome to FT!