As others have said, the constitution heavily discourages this by giving two senators to each state, regardless of population. Now if you somehow had another proposal go through whereby there's a heavy incentive to be a bigger state, another dynamic might play out. I'm not sure what incentive this would be: maybe senate allocation by population, block votes in the Senate, state governments choose the presidency on account of size, etc.
Assuming there was a benefit (in terms of power or economics) these are the states that have historically been similar to each other and geographically reasonable:
- New England (Anglo culture, commercial, Atlantic)
- New York, New Jersey, Eastern Pennsylvania (ethnically diverse, commercial, industrial, Atlantic)
- Virginia, Delaware, Maryland, North Carolina (tuckahoe culture, slave societies, tobacco economy, Atlantic)
- West Virginia, Kentucky, Tennessee (Scots-Irish, some slavery, inland)
- Western Pennsylvania, Ohio (freesoilers, wheat/corn, inland, industrial)
- Indiana, Illinois (freesoilers, wheat/corn, heavily agricultural, inland)
- Wisconsin, Minnesota (Scandinavian, dairy farming, tough winters)
- South Carolina, East Georgia (Caribbean culture, slavery, rice economy, Atlantic)
- Georgia, Alabama, Missisippi (heavily slave-based, cotton plantation economy, new money)
- Louisiana Southeast Texas (heavily slaved-based, sugar plantation economy, big oil reserves)
I've got bored, but you get the picture.