IMO there are 4 fully reasonable ways to look at it, which I'd accept from a GM as house rulese without question:
1) Hybridized effects are equal parts, and any one realm effect targeting affects them proportionately. (Which is how RR mods, or spells that affect RR mods work.)
2) Hybridized effects are equal parts, with some mixing, so one realm effects targeting them affect both the pure targeted portion, and the mixed portion. (Which Rasyr seems to be saying.)
3) Hybridized effects mix, but are so interdependant that if you remove or block one realm, the whole thing falls apart.
4) Hybridized effects are fully mixed and unique, taking on their own characteristics and are only affected by exactly the same hybridized effects or arcane. (Which would be quite hard to defend against or dispell)
The logic I laid out up top covers 1 for cancels, and is also the way RRs work.
I beleive rasyr's version covers 2 for cancels, but if that were true, then a +30 channeling RR mod should give you +20 (2/3) vs Channeling/Essence rather than the +15 (1/2) that it does currently. . if a cancel channeling spell affects both the pure channeling and the "mixed" channel/essence portions, missing only the pure essence parts, then a resist channeling spell should have EXACTLY the same treatment.
#3 would be a simple answer, it'd say "If the cancel spell has any realms in common with the target spell it has full effect". . .but then your RR bonus vs hybrid would be "The higher of the two realms."
#4 would make hybrids and arcane kinda nasty. . .and is the situation as of right now in terms of cancelling magic without a rules call by ICE. This doesn't mesh with the logic of how RRs work either.