If cloud9 can pull out the underdog victory over SSB, then I think they can beat SSW.
The point of underdog victories is that they aren't repeatable. If Cloud 9 has 30-70 odds against Samsung Blue and manages to pull out a win, that doesn't change the fact that they had 30-70 odds, and it doesn't change their odds versus Samsung White.
I'd also like to point out that Ozone were the favorites against Blue in Champions Spring. Anything can happen in team kill matches, because the teams scrim each other so often. It's not really fair to take the results of Samsung Blue vs. Samsung White and assume that it's indicative of which team is stronger on the international stage, against opponents that they've never played against before.