Personally, I have never been a huge fan of taking on Cannon characters. Largely because I feel we would fail to portray them correctly.
I have, in the past, taken on a character or two (IN Daedalus - we currently know that the Director is Khan Noonien Singh - and I have written an episode That involves a meet up with Enterprise - with a major part for a cannon character)
However, a small handful of exceptions aside - I personally try to avoid Cannon characters as much as possible. I believe we are all creative enough to come up with our own characters and stories - and as such, we should