You're probably right about sestito, without roster changes him and dorsett will be more or less interchangeable most likely.
I don't see Matthias going to the 4th line though. that makes a big difference for horvat. Benning said early on vey may be started on the wing as well. So if the Canucks do end up playing vey on the wing, and horvat gets at least 9 games, opening night roster could be:
D Sedin - H Sedin - Vrbata
Burrows - Bonino - Kassian
Higgins - Matthias - Vey
Horvat / Richardson - Hansen
I know people say 4th line minutes are bad for development, but if it happens that horvat earns a longer look after preseason, I think all 4 of those lines would be getting a fair share of minutes.
I also like the idea of having horvat with Richardson and Hansen. They both skate well and have a lot of experience, they would be good linemates to start learning the NHL pace with.