CP birds rusting away in YXE and YYC.
 

The real cost of the AC/CP consolidation can be seen on the runways in several airports where the "excess" CP and AC planes sit and rust to this day. Logos are all painted off, well with one coat of paint but it is a shame to see these planes not being put to work. At YXE there are at least 15 smaller regional styled planes and the same is true in YYC.

The capacity that has been taken out of the AC system is too evident.

What kind of aircraft are they? 737's F28's

F28's at YXE. No 737's.

Why don't these planes get sold if they are not being used?

They don't make economic sense to operate. They are less fuel efficient, require more frequent maintenence and are less attractive to consumers than more recently-built aircraft. It would be extremely tough to fly them at a profit in today's market environment.

Are there any storage costs to have these planes "parked" there?
Who pays the bill?

I have fond memories of CP F28's on RDU-YYZ and RDU-YOW, especially after the ex-BA seats went into F. But F28's are hopeless. Only about one-third of the F28's built are still flying, generally as private jets or in third-world countries. Some of CP's F28's were built in the early 1970s. There are plenty of F100's and F70's built in the 1990s that could be pulled out of desert storage.