Please go through the publication link below, each time you bring in stuff you need the "Goods to follow list" and a CBSA officer will mark the items you have brought in until the list if exhausted, the document doesnt specify the time limit, the only thing you need to make sure of the following
"To import goods duty- and tax-free, Settlers must have owned, possessed and used the goods prior to their arrival in Canada and Former Residents must have owned, possessed and used the goods for at least six months before returning to resume residence."
Secondly,
"If you import goods duty- and tax-free into Canada and if you sell or give the goods away within the first year of importing them into Canada, you will have to pay any applicable duty and taxes immediately. If you divert the goods for commercial use, the same rule applies."
"Immigrating or Returning to Live in Canada"
cbsa-asfc.gc.ca/publications/pub/bsf5113-eng.html