All states in the US have a system that is roughly equivalent to the three-branch system of the Federal government: an executive branch, a legislative branch, and a judicial branch. The exact form of each may be different, but the overall architecture is the same. If you want to call this a presidential system, so be it.
It could theoretically do so, but I can’t imagine that the residents of a state would ever vote to go that way, nor can I imagine them wanting to have an electoral college.
If a state did try to switch to a parliamentary system more like Canada’s, a 2/3 he majority of people in the state would have had to modify the state’s constitution to make the initial switch. Suppose they did? Somebody in that state, or more likely the US Department of Justice, might try to bring suit against that state in the US Supreme Court (SCOTUS), arguing that the new government was not “Republican”. So, if it ever happened, SCOTUS would have to decide.
But it is as likely to happen as it is for Canada to decide it wants to be a absolute monarchy.
Why would you make that assumption? It’s easier to put together a government when everybody knows what to expect. And remember this quote from article 4.:
The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.
In effect, this allows the Federal government to set up a provisional state government before a Territory turns into a state or states. The Federal government naturally sets up a three-branch system. The provisional (“territorial”) government then eventually turns into the state’s government. Very little chance, then, that a state will get far away from the Federal pattern.
In short, most state politicians think that the Federal architecture is pretty reasonable, despite its flaws, and works better than anything else out there.
What is interesting is that the Federa government is so substantially different from its own ancestor, the British parliamentary government. We have ample evidence to show that this comes directly from dissatisfaction with the British parliamentary practice of the time.
By the way, state government is not as uniform as you might think. Nebraska, for instance, has a one-house (unicameral) legislature which is non-partisan. The link explains this in more detail.
Every state has a governor who is directly elected, although the details of the election process may vary from state to state.
Every state (except for Nebraska) has a bicameral legislature. I don’t know the “upper” house is always called the Senate and the lower house the Legislature, but this hardly matters. They are all directly elected AFAIK.
Every state has a top-level court. Beyond that, you’ll find that there are a variety of court systems in use, though probably not 50 different ones. In the US, the judicial architecture has changed over time and continues to change, responding to changes in law and population.