From what I gather UA 1K is a better deal than AC SE and probably can be earned with fewer $ since TATL/TPAC T fare introduction. UA 1K has really good 1-way and RTW redemption if that's something you're interested in. As long as you're *G you'll get MLL access anyway. In Canada I strongly advise you getting NEXUS/Global Entry to clear customs/security line, worth every penny and faster than Priority security line (and can save yourself from missing tight connections)

Since residing in the US, I've flown UA/US domestically to get AC miles, and flew AC/*A combo out of US via YYZ to claim eUpgrades and play Aerolotto, thankfully with excellent yield despite being a lowly E in 2012. Fortunately for me, flying out of USA via a Cdn hub booked on AC.com still has fairly decent T+ fares (yes it's higher than before but with the right dates can be done still competitively vs TATL directly from NYC area).

If you do quite a bit of TATL/TPAC flying in 2013 (I see you did one TATL, one TPAC in 2012), SQ most fares and LX S fares and above get you 100% status on AE. I try to avoid UA on TATL/TPAC b/c of the horrible Y product. Recently, found good J deals on TG and OZ which gets you 125% status on AE.

Another factor to consider reaching A50 in 2013 is fly TATL/TPAC when they have the 50% bonus status promo like they recently offered in December. Can get you >50K much more quickly.

Ultimately, deciding between UA/MP and AC/AE comes down to:
1) How many flights you will fly UA vs AC that get you 100% miles?
2) How much do you value eUpgrades and whether you feel you will get it most of the time?
3) How much AE points do you redeem and how do you accumulate your AE points besides flying? Given you're based in YYC it'll be hard for you to get a US credit card to get UA/MP miles. In the US I can use SPG AMEX to convert to AE points 1:1, and Chase Sapphire preferred VISA to get convert to MP points 1:1.
3) How much are you willing to re-route creatively to get the 100% miles?

Judging from my research, it doesn't make sense to pick UA/MP unless you'll be 1K since upgrades are not possible internationally (except to Latin America and intra-Asia at UA75 Plat) and there're too many UA75 Plat and UA1K to get the free domestic upgrades in busy domestic US routes to make it worthwhile.

GT