If the French space agency (when looking for a new site for their
spaceport in the mid-1960s to get away from their existing site in
Algeria) had not chosen French Guiana in which to put the new
spaceport, would it have chosen present-day Suriname or Guyana (given
similar geographies to French Guiana)?

After all, the French did investigate some sites in non-French areas
like Brazil, Australia, Sri Lanka, Trinidad, and Somalia. And Italy
did install a space centre in Kenya (not a former Italian colony).

For more reference, see the following page from the French space
agency:
http://www.cnes-csg.fr/web/CNES-CSG-...nch-guiana.php.