Need to be mindful that Power Pages is still Preview (so not recommended for Production systems). Power Pages is going to be a super set of PowerApps Portals, with PowerApps Portals being 100% compatible (i.e. not migration). At the moment except for probably the Designer/Editor behind the scenes everything else is pretty much PowerApps Portal.
Not sure what happens with the Power Pages trial wen it expires, worst case I am guessing you could use the configuration migration tool to move it.