Forget about agents right now. Your focus now should be on promoting Book I and polishing Book II simultaneously, and then move on to promoting Book II and writing Book III simultaneously. Don’t drop the ball on those crucial things because you’re futzing around with querying. There’s nothing an agent can do for you until Book III is ready to be signed. Low sales for your trilogy because of lackluster writing or slapdash promoting will torpedo your chances with agents and other publishers down the line. There are other reasons for low sales, but you can control these two—so do! Writing the best books you can and promoting them to the best of your ability is plenty for your plate. Agents will be open to signing you when Book III is written, as long as you’ve got a sense of projects you want to work on down the road and hopes for your larger career.