If you have decided to move from Blogger to Wordpress, you’ll notice that WordPress would change your URL structure (often known as Permalinks or slugs in WP).
There’s however a simple solution to force Wordpress to use the same permalinks as created by Blogger - it involves changing a line of code near the wp_insert_post function in the blogger.php file available in the wordpress/wp-admin/import/ folder.
Arpit has created an easy-to-follow guide on implementing this change in Wordpress here. [should work on Self hosted wordpress blogs]