So it seems Air Canada is making a special offer on upgrades for the rest of the year. According to the offer page, we can upgrade "closer to [our] flight date" (sic). They really mean earlier (which is farther from the flight date, not closer). And for flights under 1500 miles , there is apparently a possibly to upgrade for "less" (sic) credits. That is, fewer credits. (Edited to remove erroneous material) So, earlier upgrading and lower number of eCerts for short flights.