Giving it two senators, and as many representatives as California, would be of massive concern to annexation-hawks - to the point that they have to not be thinking to even consider it.
Didn't think about this, but a new state would lead to a reduction in representatives for high population states like California because of the cap on the house of representatives. California would go from 52 -> 46 reps if my math is right, which is also how many the megastate of Canada would also get.