There's only one annual travel credit. Yes, since it's based on a calendar year, you can claim 2 credits your first year of card membership, but it's not accurate to suggest 2 annual travel credits is a benefit of the Plat.

If that's all you want, then sure, alternating between these two cards could work for you. Not sure it's the case for most, however, especially as many of us look to find ways around Aeroplan's ridiculous scamcharges and limited availability.