Hello franmc,
WPSiteSync can be used to sync content from one site to another, it does not matter if you are using a multisite, as long as you enter the exact site URL you want to sync to in the WPSiteSync settings. Please note that WPSiteSync should not be “Network Activated” on a multisite environment. Instead, install the plugin and activate on each individual sub site that you need to use WPSiteSync on.