We do not know about the country where the Maretime Bay is located, we only know that the area around the city of Maretown has extensive autonomy, but anyone who studied the city’s nature and technological condition knows that this is a very small part of an integrated state that may have included the entire east coast of Equestria or the southern part. It is possible that the Maretime Bay is part of the older duchy of Maretonia from the G4, because the name is inspired by Macedonia in our world - which is located in the Mediterranean region. And the Maretime Bay has inspiration taken from right there. The Old Macedonia one hundred and fifty years ago was a mountainous country all the way down to the coast of the Aegean Sea.
Idea.
If Maretonia is the nation where the Maretime Bay is located from the G4 Equestria, it is possible that it will continue to exist in the G5, but not as a duchy. We do not know where the various nation states and states are distributed in G4 Equestria, as no effort was ever made to create a political map of the land of ponies - possibly because Hasbro does not want any politicization. If Maretonia is Macedonia, the terrain around the Maretime Bay is not out of place as there is a large bay also in the Aegean towards Macedonia, “the Thermaic Gulf”, with mountains that continue inland from the coast, and Horseshoe Bay which is so large that it almost is like an ocean, partly connected to tropical climates to the south.
The Hayseed Swamps appear to be a wetland inside the southern part of the bay that is accessible from the northwest rather than along the bay coast, suggesting that the foremost part of the southern bay is also solid ground. It is little known that there were wetlands inside the coastal country in the Thermaic Gulf where malaria was a major problem, until the dehydration through human intervention. For the ponies, it will be natural to avoid the inner part of the bay coast facing the Hayseed Swamps through the use of boats, and then Baltimare will be a natural harbor. In addition, the lighthouse in the Maretime Bay means that there are several important shipping lanes along the northern bay coast and the east coast from north to south, among other things to cross over to the south.
If there was a duchy there, which could control the trade routes from the country and then the shipping traffic in the great bay, it would be in line with the history of our own world where such fiefdoms were often created on economic activity. On a map of Maretown in the G5, it looks like this city was important in ancient times, possibly it was a fortress where the skyscraper is now located. Maybe that was where Maretime Manor existed, at least not far away, in the IDW FiM # 98. From this issue we know about the Crystal Sea with several tropical islands on the east coast of Equestria, which is probably located between the Horseshoe Bay and the coast facing against the Peaks of Perils and the Forbidden Jungle. There may be many islands there and special topographical conditions that create whirlpools, but also fixed water flows that the ponies utilized without the use of motor or muscle power.
The Duke and Duchess of G4 wore attire as a cultural affiliation about which realm they come from, and their culture seemed to be inspired by Southern Equestria with Anugypt and Mesoponytamia - and there is a trade route on the edge zone between the jungle regions in the northeast and the desert regions in the southeast . Where a colony of kirins was erected in the Peaks of Perils along what may be a very ancient connecting road between older civilizations. It is possible that Maretonia was much older than modern Equestria as a link between the pony states on the east coast and southern Equestria, and this gives the dukes an advantage when the royal sisters centralized Equestria after Discord was defeated.
Maybe Maretonia never disappeared after the end of the G4, so Sunny and Hitch can be maretonian citizens. But if this is true, it could mean that the Pegasi empire can send military forces there in search of the Mane 5 without risking a major conflict with possibly the more prosperous and stronger East Coast states. Maretonia remains a marginal state vulnerable to much stronger powers. And we know from the last trailer that pegasi forces had forced their way to the Maretime Bay, where they came into battle with the earth ponies.