cinnamon isn't gonna dissolve into the beer...hopefully it sticks to the sediment.
if it doesn't, you'll be drinking little clumps of cinnamon which would taste aweful.
if you really want some cinnamon in there, I suggest you get whole stick cinnamon, steep it in a cup of hot water for 15 mins (this could be the same water you put your priming sugar in to dissolve it). steep it hot...less than 200F but above 150F.
good luck.