You forget that Britain and Canada also directly participated in the Manhattan project. Then they were locked out by Truman in 1945 and it took them another 7 years to develop their own nukes. It's just not that simple or straightforward.

Ukraine might have been in much better spot in some ways (they actually had functioning nukes) but in other ways it was simply infeasible politically (Russia was closer to being an "ally" than and adversary back in those days) and obviously economically unjustifiable.