Good question, but given that Cdn+ ceases to exist as of December 31st/January 1st I suspect the following scenario comes into play.

All we Cdn+ members -- if we've sent in our correct Aeroplan information to Cdn -- will automatically become Aeroplan members -- or have our points transferred tothose existing Aeroplan accounts -- and assume the equivilent level in Aeroplan as we have in Cdn+ for the balance of the membership year. In late February we will then assume our earned levels for the following membership year.

Thatsays to me that if the person is Gold now, s/he will become Elite for the two months of the new year, and thus should be eligible to use those upgrade certificates if the fares are appropriate.