Just a word of warning, there is a toll bridge on the most obvious route. You normally pay online, but you can't do this in a hire car, you have to call them and pay by phone - not later than the day after crossing.
https://www.merseyflow.co.uk/how-to-pay-for-a-crossing
While the A55 is certainly the fastest route, there is probably more interesting scenery on other routes. Although you may end up admiring it from behind a tractor....
2.5 hours at LPL should be more than enough.