To get through the tutorial on easy just choose the Warrior and hit F10 for every battle.

The problem is that the province guards are not complete pushovers like most of the rest of the encounters of the first map, especially if you're at an easier difficulty level (at easy difficulty, neutral armies are weakened when facing you but not the opponent's armies, so it's easy to get lulled into a false sence of security, and then getting a hard awakening when you face the enemy)
Might be especially true with a wizard, since you don't have access to powerful spells on the first map.

My advice : wait till you have some money, then go for it! It's very likely that you won't win. You'll be slaughtered. But you will hurt them bad. Then you raise your hero at your castle, hire a new army, and attack again. The defenders won't have the time to heal completely, so you should win that second battle.
That's the way I finished the tutorial with my "commander" hero, anyway. :)