I really doubt that an old plate number can in general be reissued
, since I've never seen it done with normal plates before, in Ontario or Alberta.
There is at least one exception: amateur radio operators in Alberta have had plates issued to them (not for trailers) with their station call sign, after turning in old expired plates from a previous holder of the same station call sign who had plates in their name. For example, someone gets VE6ZYX and gets a plate to match, then later drops his radio license
and lets the plate expire; years later, some other operator gets VE6ZYX, begs the first guy for the plates, and turns them in at the motor vehicle licensing branch so that they can issue new plates showing "VE6ZYX" with assurance that there won't be two sets out there.
The amateur radio operator situation is certainly an exception to the normal rules (they got custom plates years before they were generally available), so I wouldn't count on it for ordinary plates.
Many owners of older cars run a long-expired plate on the front of their car - normally for the year the car was made - and a current legitimate plate on the rear. This works here in Alberta because front plates are no longer used. So... it might be okay to display the old plate as well as a new plate, if
the old one was clearly expired and there was no confusion... but that's just a guess.