Similarities
1) both Renaissance and Baroque era music were what is known as "polyphony," meaning they used used layered or harmonized melodies
2) the similarities of medieval,renaissance and baroque period is is usually they have a monophonic instrument
Difference
Renaissance music consisted of smooth regular flow of rhythm while baroque music was comprised of a metrical rhythm with varied motion.
Medieval music was mostly plainchant; first monophonic then developed into polyphonic.
Renaissance music was largely buoyant melodies.
Medieval music was mostly only vocal while renaissance music was of both instrumental and vocal; flutes, harps, violins were some of the instruments used.