I've listed everything in "miles per hour" (mph); multiply by 1.6 to translate the figures into kilometres.
Whilst it comes from 100 years later, the British Army's Field Service Regulations for 1914 give comprehensive statistics for a regular army moving through territory with at least a basic road network. The FSR stipulates road marching speeds of 3 miles per hour for foot troops, 3.5mph for mounted troops (this includes periods of walking whilst dismounted - if they remained mounted all the time, it was 7mph), and 2.5mph for wheeled vehicles. These rates included short halts every hour and a typical day's march was around 15 miles (6-7 hours, depending on the make-up of the force), although a forced march could double that, or occasionally even triple it (the British Light Division famously marched 42 miles in 26 hours to reach Talavera). Daily distances might be extended or reduced slightly in order for troops to reach a fixed objective - eg a river crossing, the next town, or the outskirts of a large wood.
Typically, there would be a rest day for every 3-6 days of marching, depending on the state of the roads (including how much military "traffic" it was carrying), the fitness of the troops, the availability of food, and the climate. Heat would affect the time of day at which marching took place, both to avoid fatigue/sunstroke, and to minimise dust (just before dawn until noon was a common marching period in summer and in places such as India, with the hottest part of the day - noon until 4pm - being avoided).
Obviously, the speed of a column was dictated by the slowest element - usually the artillery and baggage. However, if your armies are moving three squares a day, then a square would equate to 5 miles/8 kilometres or so - although for a short campaign such as the 100 Days, perhaps you could be generous and make each square 10 kilometres to keep the maths and map scale simpler.
Hope that helps.