The things is, CNs are meant to reduce micromanagement and increase the amount of wars in the colonies. Siberia is colonized by Russia and maybe by the Iberians (I doubt this will happen anymore in 1.8).
So, since there's basically 1 colonizer... CNs are kind of useless, what wars are there to provoke?
I'd actually do something else - I would make the provinces closer to the Urals harder to colonize so that Russia has a hard time getting to the Pacific until very late tech levels, when colonization should go much faster.