If you are in Canada, the chance of a good last minute "deal" is virtually nil this year. We too, usually take the last minute route as we have been to Punta Cana five years in a row. However, since there have been so many seats available "last minute", the Canadian tour operators cut back their inventory by 30% this winter so they weren't having this problem!!
As a result there will be little available if you don't book now. Many resorts are already sold out for good travel dates. For example in early November, we wanted the Riu Bambu or Palace for the last week of January/first week of February and it was already sold out. Many others were on the verge. I suggest you book now as you are otherwise likely to be disappointed. Fortunately, the DR -- particularily Punta Cana -- is still a good "bang for your buck".