What is the transfer function of an LCL filter?
For control purposes you need to linearize the system around a single operating point.  Considering the synchronous DQ frame, the grid voltage is DC and therefore can be neglected.

Do not replace the grid voltage with a resistor.  You are mixing the power delivery circuit with the filter circuit.

The resistor will cause huge damping where you don't want the damping to be.  And your inductances are way too small.

First, you need to select the maximum current ripple.  This will set your inductance.  Then you need to select the shunt capacitor value based on maximum current harmonic distortion that is allowed into the utility.  

For stability purposes you need to add passive (resistor) or active (measurement + controls) damping into the system.

Inductance L2 could be partly physical and partly the inherent grid inductance.  So you need to make sure the design and controls are stable for any grid output inductance (which varies based on the grid loading and time of day).

So, to answer your question:

You need to control the current so calculate the inverter voltage to grid current (L2) transfer function.  No reason to calculate voltage to voltage transfer function since the grid voltage is established by the utility.

\$ \frac{I_{L2}}{V_{inverter}} = ... \$

Btw. this is a simple sophomore level calculation.  But the implications, the control and other dependencies make it a grad-level problem.  Good luck!