I honestly think both would be fine on the Nice course. On one hand the 20 km or so in and out of Nice are very flat and fast. On the other hand the rest of the course is all ups and downs with long moderate uphills and fast, twisty descents. Unless you know the course extremely well, you will have to constantly get out of your aerobars as most turns have no visibility.

Most pros will be on road bikes. Many faster age groupers will be on tri bikes.

Edit to add: did the race in 2008 on a tri bike, 5:28 bike split.