Is the maximum load of my circuit panel split evenly between the two legs?
What you have is 240V @ 200A, with a center tap neutral giving you a neutral/center return.   

This is single phase with a center tap, it is not conventionally called "two phases" but rather "two poles", L1 and L2. 

If you fully load it, you will pull 200A down the L1 pole and necessarily by the nature of current flowing in loops, 200A down the L2 pole.   

You can pull any amount of current you please down the neutral. Since the neutral essentially breaks the big loop into two little loops, neutral only pulls differential current: if you pull 40A across L1-neutral, and 30A across L2-neutral, then neutral flows 10A.   If you draw 200A down L1 and 0A down L2, neutral carries 200A.  There is no combination of draws that can make neutral draw more than the largest pole. 

If you're now thinking "I can power two 120V circuits with a common neutral", you are correct and that is called a multi-wire branch circuit.  It's fallen out of style in the age of GFCIs, because it requires GFCIs which are special.   The three conductors in a GFCI only carry two wires' worth of current, so only count as 2 wires for thermal calculations.