Linked pages from plugin on front can’t see $wpdb

I would do something like this:

<a href="https://wordpress.stackexchange.com/questions/42287/?xp=<?php echo $row->BrExpress; ?>">
<img src="https://wordpress.stackexchange.com/questions/42287/images/full_menu_icon.gif" 
alt="See this store menu" class="menuimg" /></a>

And then to load the page when the link is clicked:

function load_the_menu_page() {
    if(isset($_GET['xp'])) {
        global $wpdb;
        // retrieve database info here

        return $info;
    }
}
add_action('init', 'load_the_menu_page');

Note, this is just a sample. If you do something like this you should greatly improve it. You will want to use a nonce and also name your functions appropriately.

It’s still not very clear as to what exactly you’re trying to do, so if this isn’t close, please try explaining more.