The Raptors have a happy problem: we drafted Ross and he actually looks very good. Sweet stroke, lots of speed and leaping ability, good defender even as a rookie....lot's of potential for a star shooting guard. We already have a pretty good shooting guard in DD, who is close to a 20 point scorer already, pulls down 5 boards a game and get a couple assists. Demar is 2 years older but still has some development to go through and he could easily get to be an all star in the east.
In my opinion having two guys as similar as these two who play the same position is great...if you are winning games. For us, we have so many holes I don't see how we can keep two guys who have high trade values on the team when only one of them is likely to be part of our future starting 5. So who do you move? Ross is younger, he's athletic and already seems more skilled, though he'll never have Demar's size. Derozan is already a good player in his own right and is a bit more proven: Ross could still bust. One thing to consider here is when we intend to compete. If we are rebuilding again, maybe Ros is better so he can grow up in the new system. If we want playoffs next year, maybe you want someone a little farther along.
I would trade Ross before DD, I'm big on having NBA proven talent and Demar has at least shown he can play in this league at a high level.