display titles from one custom post type in meta box in another custom post type

I have a custom post type named “supplier” and another one named “customer”. I’d like to be able to select from a list of existing suppliers in a meta box in wp-admin on my “customer” custom post type add/edit page.
Can this be done?
I have made the meta box with a html select ready on the “customer” add/edit page.
I need to make the functions.php spit out an array of the “supplier” custom post type titles into my html select.

all help appreciated/Thanks