That is primarily in Crimea, Lugansk and Donetsk provinces (southeast, Russia calls it the "Donbass"); which, Russia already has.
I mean, it's also anywhere East of the Dnieper River... except...
Since Putin stole Crimea, Lugansk and Donetsk... even Russian speaking or Russian leaning Ukrainians (east of the Dnieper) are enraged at his moves and his current threats. You might get some saboteurs from the area... but the overwhelming attitude is intensely anti-Putin at the moment, even there.
I mean, we'll see what happens when the tanks start rolling in...