I was looking through ac.com and noticed this one show up

ttp://www.aircanada.com/shared/en/aco/flights/pop_faretypes.html

10. Accumulate Air Canada Status Miles as indicated for travel within Canada and between Canada and the U.S., including Hawaii, on all scheduled flights operated by Air Canada, Air Canada Jazz™ as well as Air Canada codeshare flights operated by Air Creebec, Air Georgian Limited (doing business as Air Alliance®), Air Labrador, Calm Air, Central Mountain Air and Pacific Coastal. Aeroplan Miles earned for distance flown on Tango fares do not count towards Air Canada Top Tier status. For more details on mileage accumulation, visit aeroplan.com.
Fee for advance seat selection is distance based as follow:
Zone 1 (0 - 350 miles ), Zone 2 (351 - 1000 miles), zone 3 (1001 or more )
zone 1 $15
zone 2 $17
zone 3 $20

Now I wonder what happens when someone that paid for their specific seat has an equipment change?