Don't you just hate putting gesso on raw canvas? Well, here's a tip that really works for me.
I started using a 3 inch foam rubber roller. It comes in a kit that includes a tiny plastic tray that doubles as a storage container. You'll find it in the house painting section of your local home improvement store - the one I found is made by Rubbermaid but there may be other brands available.
After putting a small quantity of gesso into the tray, I roll it on the canvas or board. It's so quick you'll actually enjoy the chore, and the best part is that you get very even coverage without the annoying brush marks -- unless you want brush marks, that is. I usually do two or three thin coats, alternating the direction each time. Then, if I want more texture, I'll use a gesso brush for the last layer.
Clean up is easy, the roller lasts a long time, and replacement foam is available.
I can tell you, this really saves my shoulder when preparing a large canvas.
One warning, though -- this method splatters gesso around, mostly on your hands and arms, so be sure you protect any surfaces that are in the line of fire. Those little dried specks of gesso are a real bear to clean up...