From PlayStation Universe: “The Mega Man X Legacy Collection features eight of some of the best retro titles around. We compiled a guide to help you get through each of the bosses and in the easiest order. The trick to defeating each boss, is to find the easiest to defeat and then take the new weapon acquired from them and taking on the next boss whos weak against youre newly acquired weapon.”
Source: N4G PC Mega Man X3 Boss Guide and Boss Order