Is this debt still collectable even if it was written off in sale of the property to a new owner?
absolutely

Is the breach date the actual date the apartment was vacated or when it was turned over to the collection agency?
it would be whenever you caused the debt to become due. A collection agency cannot alter the date that the debt is to be removed from your CR.

do not mistake a date they purchased the debt and as such, began reporting as owners of the debt as the original date of indebtedness. What you are seeing may simply be the date they purchased the debt. The total time the debt can be reported is still 7 1/2 years from the original date. If it is still being reported after that date, notify the CRA.