Let’s do the United States.
The initial American Revolution fails, but many of the Patriots decide to head out west, heavily settling the area between the Appalachian Mountains and the Mississippi River. A second rebellion, centered on this frontier region, eventually breaks out and wins some limited success. An independent American republic is formed in most of our timeline’s Midwest, Appalachia, and the interior South. While bound to the east and north by a still-British New England, Tidewater region and Canada, and to the south and west by Spanish Florida and Louisiana (though they are eventually inherited by some independent state or states), access to the Great Lakes (not oceans or seas, so this technically fits the stipulations of the OP) and favorable treaties allowing economic access to the Mississippi River and the port of New Orleans means that the country escapes most of the drawbacks of being technically landlocked.