Russia wants a multi-polar world, without alliances, where the big guys can bully the small guys. That's why they support Brexit and Calexit and Catalonia's secession from Spain andsoforth. That's why they hype any sign of discontent in Europe.
Russia does NOT want a world where the small guys work together to stand up against the big guys.
(Why does Russia want such an alliance-less world? Because pretty much nobody wants to be in an alliance dominated by Russia. For example, Russia wants to create an international economic zone similar to the Euro, except there are no takers willing to join.)
Merkel from the conservatives? Wants a stronger Europe.
Schultz from the social-democrats? Very, very much wants a stronger Europe.
The Greens? More Europe for more civil-rights, peace and environmentalism.
The Left? More Europe for more civil-rights and peace.
The Free Democrats? More Europe for more civil-rights and peace.
The AfD? Less Europe for less immigrants and more nationalism.
The only party that is to Russia's liking is the AfD. And they are political pariahs (because no other party wants to work with them), polling at 10%-15%.
Even if Russia were to take the risk of manipulating the election, the pay-off would be minuscule.