Just to add to some of the other comments

NEXUS rules for faster transborder clearance

Tango fares have been showing up for EWR-YYZ and on occasion the LGA-YYZ, but often they are the same price as the T+ fares.

If you want to do a status match to get priority boarding and lounge access in Toronto, you could always get USAIR, and then once you have enough qualified segments on AC, you would be an Elite member, good enough to get you into lounges on both sides -- albeit the UA lounge in LGA is a half a terminal away -- ok sounds dramatic, but its about 5 minutes.

If route frequency is important, AC has twice as many flights from YYZ-NYC, through LGA and EWR than AA (LGA and JFK).

As pointed out before, AC does offer short-haul flights @ 15k points (25K for Biz) and YYZ-NYC is on this list. My points are mostly used for this sector as Aeroplan does offer a lot of availability for this route. The downfall is the high redemption charge (approx $110).

Finally, if he were a diehard FF, he could do NYC-IAD-YYZ on UA! I have booked this a few times, and usually on the way back, the agents look at this and try to get me on a direct flight!