Ok, so I managed selecting the checkbox with some jQuery added via functions.php:

//Select sector in posts filter
add_action('wp_footer', 'sectorpostsfilter');
function sectorpostsfilter(){
	if (function_exists('get_field')) :
		$sectorobject = get_field('taxonomy_sector');
		$sectorid = $sectorobject->term_id;
		if ($sectorid) : ?>
		<script type='text/javascript'>
			jQuery = jQuery.noConflict();
			jQuery(function( $ ) {
				$('.sf-item-<?php echo $sectorid; ?> input').prop('checked', true); 
			});
		</script><?php 
		endif;
	endif;
}

And by altering the query within the template:

<?php 
if (function_exists('get_field')) :
	$sectorobject = get_field('taxonomy_sector');
	$sectorslug = $sectorobject->slug;
endif;
$loop = new WP_Query( array( 'sectors' => $sectorslug ) ); 
        while ( $loop->have_posts() ) : $loop->the_post();
			get_template_part( 'loop', 'post' );	
	endwhile; wp_reset_postdata(); 
?>