HERO normally put a list of 'spectator points' on their website nearer the event - I don't think it's there yet. From that you can normally guesstimate an approximate route. It's a bit of detective work but some Googling can sometimes work e.g. you might come across some district / parish council meeting notes online that mention a route re permission etc.
The route this year is to the west of the UK and into Wales. Saturday night is in Chester, Sunday night is near the borders so Sunday may be your best bet but whether or not they work their way the 'proper side' of the Pennines is anyone's guess. Yorkshire is popular with these rallies (understandably so) whereas they don't normally bother with Lancashire (who would?) - sorry couldn't resist!
Alternatively they may keep west and into the Lake District but within reach from your location.
As said best bet is a lot of Googling close to the day.