BonkJr said:
Is it necessary to provide a Notorized letter of invitation to invite my wife's niece to visit Canada for a couple of months?
It doesn't need to be notarized. Just provide the necessary documents when submitting the application.
if you're a Canadian- you can provide a copy of your birth certificate, T4, NOA, Payslips and COE and if PR- PR card and same as the things I mentioned.