-- Last Updated: Jul-02-13 5:12 PM EST --
I've always used Thule square bars and components. I don't like the Yakima round bars though others swear by them (I would judge more kayak and canoe haulers use Thule, though). Currently I use Thule bars attached to the factory bars on my Subaru Outback and on a Hyundai Santa FE, which is more similar in height to your Forester. I do have J-racks but only use them with my super light folding frame kayaks and a replica skin on frame so they are cradled on their sides. For hauling plastic kayaks and canoes (and I usually have two on the roof) I just have plastic pool noodles wrapped around the bars with duct tape.
To load each boat I first loop a pair of long Thule nylon buckle straps around the crossbars and slide them to the middle. Then I lift the stern or the boat, hull down, onto the rear bar from behind the car then lift and slide it up and forward until it slides over the second crossbar. Then I roll the boat over until it is deck down with the cockpit (if a kayak) centered between the crossbars. Then I grab the ends of the first strap and run both over the boat and around both the cross bar on the outside and around the factory lateral bar as well and snug the buckle down. Repeat on second strap. Do the same thing on the other side of the roof to load the second boat. I always-always-always use securely tied bow and stern ropes from the boat ends to the hooks under the bumpers as well. Even if in a rush or a short distance low speed haul I will always put the bow line on so I can keep an eye on it while driving to detect if the boat or boats are shifting position.
The load ratings on the factory bars on Subarus say 75 lbs total for the whole rack, so I am usually over that but I would bet money those ratings are "cover our asses" conservative and I have had no trouble hauling boats like this for 10 years and countless thousands of high speed highway miles.
If I was going to carry two full weight canoes on a long windy highway trip, I would probably remove the bars and lash the canoes directly to foam blocks or pool noodles on the roof (said blocks fastened with straps around the inside of the car through the open doors). Niether of my cars has side curtain air bags so I can safely run straps across the inside headliner. My understanding is that securing anything to the roof that way can cause side curtain bags to explode during a crash and hurt the occupants, but I have no expert confirmation of that.