Well I hope Britain could be excluded in this scenario since it is a sea power and would only care about Europe the if the balance of power was disrupted. France was Austria main rival during this time period, things had quieted down with Prussia until 1866 since problems could be resolved in the German Confederation. France will need to be contained both politically and ideologically. The latter is the hard part. France had a lot of revolutions during this time period, so it was exporting a lot of ideological material that would need to be suppressed. It is funny that Austria's success depends on the political stability of France!
The more disunited Germany and Italy are, the more powerful Austria would be. Letting Austria annex German territory makes this a little too easy because this could turn into a Prussia-screw timeline and it isn't like there arn't plenty of those already but if Austria beats Prussia they could take Silesia back. They absolutely could do that. Now the Italians got screwed over in OTL. The Germans at least got the German confederation but the Italians got nothing from the Congress of Vienna. Even so, Italy was unified almost too easily in OTL, it wouldn't be to hard to make an almost unrecognizable Italy from ours under the right circumstances. If Austria was the predominant power over both a disunited Germany and Italy, they would be a lot stronger.
Even under the most favorable circumstances though I can't see nationalism being delayed for longer than 50 years, so Austria will need to adapt to that or there will be a total meltdown by 1900 give or take 20 years. Nationalism was linked Industrial Revolution and both of those things are what finally killed Austria.