According to the LDS Church's “Handbook 2,” only the governing First Presidency can speak on official behalf of the church in regard to a measure such as Proposition 2.
One will not find a statement, anywhere, in opposition to Proposition 2 that actually bears the imprimatur of the First Presidency, nor any specific citation of such by other church personnel. Technically and logically, then, the very notion of “church opposition to Proposition 2” is a hoax — one that is having a significant influence on church members.
Whether the First Presidency actually is opposed to Proposition 2 is irrelevant.