There is a picture of the actual I/O structure (very simplified) in section 8.2
For typical drivers / receivers of this type, pin and ESD diode capacitances normally dominate.
I would estimate about 15pF per pin (to be safe, it is likely to be lower). Track capacitance is about 1.1pF / inch on FR-4 with a track width of 4 thou and 4 thou to plane. Do not forget to add track and via capacitance to the calculation.
So you could have quite a few of these and I2C should work fine. As ThePhoton noted, the capacitance in table 32 is the maximum permissible on the total bus.
[Update to add note on interfacing with wires]
You can calculate the effective capacitance of twisted pair at this question.