I'm guessing they would be against the unification under a monarchy of any sort.
And it bears pointing out again that they were against OTL.
If they survive past even the 1830's they are going to be in a very powerful position and probably supporting and empowering states and people that follow the republic form of government.
Or alternatively they're going to settle down and be accepted onto the European stage by the other powers just as Napoleon later was as long as they
don't pursue endless aggression against everyone.
Any such unification talks are going to probably have French backed and modeled German states that are not apt to join a state under a king.
Why does Germany have to be monarchist? And really, what's wrong with Moltke the Elder's method to resolve the French issue? It was most effective OTL.
Thus, any type of Germany is going to be smaller, perhaps some kind under Austria. I see Prussia as remaining strong, but remain simply Prussia.
...Why?
Probably Prussia and Russia remain close and eventually become some kind of counter to Republican France.
It's all about the Balance of Power. They might, if the BoP necessitates it. Then again, they might not. And really, there was a lot less idelogical Destroy the Republic! conviction than people often seem to think. Prussia were the first to make peace out of Coalition #1. Russia wasn't even a member. Russia bailed out of Coalition #2 after a few bungled efforts, while Prussia wasn't even a member. Prussia sat around twiddling thumbs for the Third Coalition, and then when she was defeated, Russia was all too hapy to sell her out.
Austria has to choose which nations she wants to be her enemy as her choice becomes side with Russia (possibly and Prussia) against France or France against If this France is going to survive then I think it's going to require some major French wanking because without a unifying Germany becoming 'too powerful' for the balance of power in Europe, that title still would be France. Not sure where England falls into here. I would wager anti-French throughout.
It does seem likely that if the French are succesful in entrenching their power in the natural frontiers and peripheral areas efforts will be made to overthrow the system of revolution, rather than that of reaction. Really, though, as I say, we can't predict the alternate diplomacy with no specific PoD.