I think that it will be 50-75 percent Senators fans if we face the Leafs. Regular season games are different because Senators fans can watch the Sens play dozens of times a year for $30, Leafs fans cannot. That's why it ends up at 75+ percent Leafs fans. The floor for Leafs tickets is higher than the ceiling for regular season Sens tickets, so they all get sold to Leafs fans. Playoffs are different because there is no substitute product. There is more demand with Sens fans, and there is a willingness to pay a few hundred dollars for nosebleeds.
The secondary market sales are a drop in the bucket right now. For example, game 1 has sold 10 tickets in the last 24 hours, and it isn't guaranteed that those are all Leafs fans.
The bigger concern is the undercover Leafs fans who are SSMs. I think the resale aspect is going to be a bit overblow and most of the invading fans will come from within.
In theory, I don't mind the split crowd, it actually could be a really fun atmosphere with normal well adjusted people - but the problem is that most Leafs fans treat it like The Purge.