Currently, Air China is offering flights in November to Japan from $601CDN, taxes in! Click here to use Skyskanner to begin your search. The search in the link are for the dates Nov.10-19th, but apparently, the 17th-26th are similar prices.
Delta, Air Canada, and American (meaning of course, you'll fly with AC if available since the others fly inferior planes and the points you'll earn with Delta and American are pretty worthless, especially Delta) have a sale for flights from Montreal to NYC (LaGuardia) from $138 to NYC and $90 to Montreal, so flights start at $228CDN taxes in, return! Considering flying on Aeroplan points would cost you 15K plus $195.60 (or 25K and $70.45), you're clearly better off paying with cash or AMEX points (22.8K AMEX points, inclusive PLUS you'll get some Aeroplan points for the flight PLUS double AMEX points), it's worth "paying out of pocket" compared to getting shafted on the taxes with Aeroplan.