It really depends how many points you need and how much you're willing to spend.

I did YYZ->JFK->DCA->JFK->YYZ as a day return tp run in November last year - it was an ok price for the points - but it wasn't spectacular - but it happened to give the 200 points i needed for the budget I had. It was a same-plane turn around in DCA which reduced the risk. Did raise some eyebrows at both American and Canadian immigration on the way out and back. I got asked 'so ... you're not even leaving Washington airport?' with really wide eyes and a shake of the head (as in 'he's mad') from the immigration lady.

The problem from YYZ is that the flights are spaced out - so a day return can be tricky. You have more options now that US Airways are included - but be aware that a good number of the US Airways flights don't have even have a business or first cabin out of YYZ. Although US Airways flights are currently providing double tier points in discount economy which is a bonus (or were 2-3 weeks ago).

Oh - and ALL AA flights out of YYZ only ever code as business - never first. So the first leg is always either 40 or 140 rather than 60/210.

M.