I recently tried to get TC to renew my Canadian IFR that had been expired for one year as I am currently flying on an FAA licence. TC will only renew Canadian IFR's that have been expired for 24 months, after this period they treat it like an initial application. Unfortunately the 24 month rule doesn't help me but hopefully it will help someone else. Some regions are not aware of this rule so you may have to call around.
Staff Instruction (SI) No. 401-001 - Transport Canada