You can buy upgrades on the transborder (ie US Canada routes):

http://www.aircanada.ca/planning/us-.../upgrades.html

Upgrades: U.S.A to Canada
Purchase upgrade certificates and treat yourself
to the comfort of Executive Class!
Enjoy Executive Class® with a Hospitality Service ticket! Move up from Hospitality Service® (Y or M booking class) to Executive Class simply by taking advantage of Air Canada's upgrade certificates when you travel on designated routes* between the U.S. and Canada.

U.S.A. to Canada Upgrades

To purchase your upgrade booklet:
Each upgrade certificate is valid for a one-way upgrade and is conveniently available in booklets of two. Certificates are valid one year from date of purchase and each booklet costs only US$70, plus applicable taxes.

To use an upgrade certificate, simply:

Ensure you have a confirmed Hospitality Service ticket in Y or M booking class for travel between Canada and the U.S.A. aboard any qualifying Air Canada or Air Canada Regional Inc.† flight.
Call your travel agent or the Air Canada Reservations number at 1-888-247-2262 within 48 hours of departure to request your upgrade, subject to availability.
Finally, present your U.S.-Canada upgrade certificate when you check in.
So simply sit back and enjoy all the comfort of Executive Class!


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* ROUTES:
Designated routes between the USA and Canada are:

La Guardia - Toronto, Montreal
Denver - Toronto
Chicago - Toronto, Montreal, Calgary
Los Angeles - Calgary, Edmonton, Vancouver
Dallas - Toronto
Philadelphia - Toronto


Note: Upgrades can only be applied to a previously-purchased ticket with confirmed reservations. Upgrade reservations can only be made within 48 hours of departure. For upgrades to be honoured, the certificate must be presented at check-in. Upgrades are subject to availability and number of allowable upgrades per flight. Upgrade certificates are not valid on Air Canada marketed flights operated by other airlines, or on charter flights, for Aeroplan® reward travel, or with promotional passes. Certificates are non-refundable and do not permit access to Maple Leaf™ lounges. Other restrictions may apply.

If you are travelling midweek, you may be buying the outrageously high Y fares anyway so, even though you can't use points to upgrade, these allow you to "buy" your upgrade.