Or can I have a familiar from one class and a bonded object from the other?
From Arcane Bloodline:
Arcane Bond (Su): At 1st level, you gain an arcane bond, as a wizard equal to your sorcerer level. Your sorcerer levels stack with any wizard levels you possess when determining the powers of your familiar or bonded object. Once per day, your bonded item allows you to cast any one of your spells known (unlike a wizard’s bonded item, which allows him to cast any one spell in his spellbook). This ability does not allow you to have both a familiar and a bonded item.
If you make a Wizard x/Sorcerer Y with the arcane bloodline for Sorcerer, you have an Arcane Bond level of X + Y. If you chose to have a familiar, it would have a level equal to your character level in this case, for the purposes of determining its abilities. Similarly, if you had chosen a bonded object it would be counted as your character level for the purposes of determining what item creation feats you can use to add abilities to your bonded item.