Officially Samsung states that the Galaxy Tab 2 7.0 supports micro SD cards upto 32GB. That is because the Tab 2 7.0 was launched with Android 4.0.4 ICS which does not natively supports 64GB micro SD cards.
Samsung later rolled out Android 4.1.1 jelly bean which was followed by Android 4.1.2 (the Android 4.2.2 is in works), both of which support 64GB micro SD cards. To make them usuable on your Galaxy Tab 2 7.0, make sure to format them to Fat32 using a PC.
Also, you need to make sure not to use any files greater than 4GB. If you do not do that, your Tab 2 will become very slow.
Also check out Galaxy Tab 2 7.0 ICS root.