The rank ordering of weather sealing is: 1-series >> 7D > 5DII = 60D/50D. Personally, I trust my 7D in the rain when a sealed lens is mounted on it, but I wouldn't trust the 5DII in anything more than a light drizzle.
Canon's warranty will absolutely not cover water damage for a 5DII. There have been reports of mostly unsuccessful claims for water-damaged 1-series bodies (with a couple of exceptions).
However, if you have a 5DII and L lenses (which is the only way to have even a partially sealed combination), the value is high enough that you really should have separate insurance coverage for your gear (i.e. a rider on your home/rental policy or a separate policy from your home insurer). In most cases, that covers any form of loss, including water damage, theft, dropping off a cliff, etc. - at least, my coverage does, with no deductible.