If you haven't paid taxes on the severance amount, you won't be getting taxed twice. RRSP is a tax deferral vehicle, not tax mitigation. By putting money into your RRSP in 2016, you lowered the amount of taxes owed in 2016. Where the money came from is irrelevant. The issue of paying taxes on your severance is a completely separate issue. Simply putting that money into an RRSP doesn't make it tax free. You still have to pay taxes on it, then your income will be reduced by that amount when filing.
