Snippet to change weight in Woocommerce Canada Post Rate Request. WooCommerce Canada Post Shipping Plugin with Print Label - https://www.pluginhive.com/product/woocommerce-canada-post-shipping-plugin-with-print-label/

functions.php

/**
 * Snippet to change weight in Woocommerce Canada Post Rate Request.
 * Created at : 10 Aug 2018
 * Updated at : 10 Aug 2018
 * PluginHive Plugins : https://www.pluginhive.com/plugins/
 * Gist Link : https://gist.github.com/xadapter/f6c84df50af11b5f952e170379933f7f
 */
add_filter( 'xa_canadapost_rate_request', function( $request ){

	$default_weight = 15;		// In kg

	$request_arr = explode( '<weight>', $request );
	if( ! empty($request_arr[1]) ) {
		$new_request = $request_arr[0].'<weight>'. $default_weight. '</weight>' ;
		$request_arr = explode( '</weight>', $request_arr[1] );
		if( ! empty($request_arr[1]) ) {
			$request = $new_request.$request_arr[1];
		}
	}

	return $request;
});