And who said that the Russians are sane people? And do you actually think, that the Russians see Americans, Europeans or Ukrainians as sane peoples?
Man, it's XXI century. You can't just build a big wall on the border and feel yourself safe. In the matter of fact, walls per se never worked (neither in Medieval China, nor in Ancient Britain). And the best defense is a good offence. That's why we are fighting against our own enemies anywhere in the world.
It mostly depends on your definition of the term "Ukrainians". And no. The absolute majority of ethnic Russians and Russian-speakers in the eastern and southern regions of former Ukraine doesn't hate their brothers from Russian Federation. Ukraine is not "Russian Vietnam" or "Russian Afghanistan". Ukraine is "Russian Canada" or even "Russian Confederacy".
America can't allow Canada join Shanghai Pact by any means, because Canada is vital for the America's safety. Therefore, even though annexation of Canada could cause some problems (including some kind of guerilla war) those problems are insignificant comparing with possible deployment of the Russian nuclear missiles there. And absolute majority of Canadians can accept that now they are living in the USA.
From other point of view, we see one nation divided by the political and economical goals and strategies. Political and business elites of the one part (mostly agricultural) wants to become an agricultural appendix of Europe, and other (mostly industrial) wants to be actually independent center of force. One side believes that a certain type of people can be abused and discriminated and other side believes in the equal rights for all human beings.
From the American point of view Quebec guerillas can be a threat, but this threat is incomparable with the potential threat of the Russian&Chinese tanks, bombers and nuclear missiles in Manitoba. Therefore, if there is a choice between US-Canada war and allowing Canada to join Shanghai pact, there, in fact, is no choice.