Welcome to History Hub
Google books has several Histories of Louisiana that can be read online
I hope this helps,
Dear Ms. Huguet,
Thank you for posting your request on History Hub!
We searched the Library of Congress catalog and located the article Louisiana as a Spanish Colony that is part of the larger presentation titled Louisiana: European Explorations and the Louisiana Purchase that may contain information about where the Spanish entered the Louisiana Colony prior to the 1804 Louisiana Purchase.
We also searched online and located several articles and other publications that might be of relevance to your research. They include:
We hope this is helpful. Best of luck with your research!