First you need to determine how far you can ride in a day. Right now, what is the average length of your daily ride? How many days off do you take in a week? Do you know how fast you ride with a loaded bicycle?
Next you need to look at a map of where you want to go, and find out how many miles you've got to cover.
If there's a significant difference, you may want to consider modifying the route or doing a lot of training.
Do not assume that if you can ride 20 miles every other day on a light racing-style bicycle that you're going to somehow suddenly be comfortable riding 75 miles each day on a loaded touring bicycle.