We booked our transfer through Dominican Airport Transfers and their website says it takes approximately 1 1/2 hours from the Santo Domingo airport to Oasis Canoa resort.
I guess it depends on the time of day as to how bad the traffic is because some people have said it takes closer to 2 hours.
We are being picked up by a private mini van (there are 6 people in our party).
We booked our trip through CheapCaribbean.com, but the transfers were over $40.00 cheaper booking ourselves through Dominican Airport Transfers .
Hope this helps.