So, the title says it all.
What if James G Blaine had been chosen as the republican nominee for President in 1876 instead of Rutherford Hayes?
I suppose one could suppose Blaine is a bit more organized and takes the nomination on the second or third ballot, before opposition can crystalize around Hayes.
How would this affect the contested election?
Who would be the 18th president of the United States?
The first question is whether Tilden still manages to get the Democratic nomination. Since Tilden's main attribute as a strong ant-corruption appeal, Blaine's nomination gives Tilden even more appeal than OTL, since Blaine was suspected of being involved in the Grant Administration scandals and even if not could be tarred with their brush.
Accordingly, Tilden might just manage to squeek by with a win. However, to avoid the controversy that errupted OTL, he'd need to win a northern state so as to avoid counting on Florida, Lousiniana, and South Carolina. I suspect that Blaine's suspected corruption and his anti-Catholic views might just be enough to tip, say, Massachusetts, Rhode Island and California. Alternatively, they only tip Massachusetts but the margins in SC, FL, and LA are less dependent on corruption.
There are really then two scenarios: 1) Tilden wins outright, avoiding any controversy and 2) the election is close as it was OTL. Really in both cases the net interesting result is the same: the specifics of the Compromise of 1877 which is largely viewed as ending Reconstruction will be changed. There is some question, though, as to whether the net effect will be too different. Both Hayes and Tilden OTL ran on platforms that would have ended parts of Reconstruction: Hayes' victory in the Ohio 1875 gubernatorial elections and his "let alone" policy toward the South won him the nomination OTL. Blaine will probably have something similar (especially since he initially opposed military government).
The interesting part would really come in 1880 and the political ramifications of a Democratic victory under Tilden in 1876. There's a slight chance that Republican resistance manages to rekindle enthusiasm for supporting civil rights, but the moment for a sucessful Reconstruction is probably gone. However, there's potential for a lot of interesting stuff: the gold-silver debate may be shifted, the rise of organized labor may be changed, the rise of the Populists is bound to be different, perhaps with important results.