woocommerce-match-canada-postal-codes.code-snippets.php

<?php

/**
 * WooCommerce Match Canada Postal Codes
 *
 * Checks WooCommerce Postal Code and removes gateways if not matching Canada Postal Format
 */
add_filter( 'woocommerce_available_payment_gateways', function( $available_gateways ){
	global $woocommerce;
	if ( is_admin() ) {
        return $available_gateways;
    }
	$user_postal = !empty($woocommerce->customer->get_shipping_postcode()) ? $woocommerce->customer->get_shipping_postcode() : $woocommerce->customer->get_billing_postcode();
	$regex = '/^[ABCEGHJKLMNPRSTVXYabceghjklmnprstvxy]{1}\d{1}[A-Za-z]{1} *\d{1}[A-Za-z]{1}\d{1}$/';
	$remove = false;
	if (!preg_match($regex, $user_postal)) {
		$remove = true;
	}
	if($remove) {
		return array();
	}
	return $available_gateways;
},20, 1);

WordPress - WooCommerce - Matches Canada style Postal Codes and removes all payment gateways if invalid match.
Add to your template functions file or in a snippet plugin.