Jim
I have been very disappointed in Thule, Yakima, and factory expensive, noisy, poor functioning racks. Looking at a picture of Subaru rack it looks like the open rail for mounting a cross bar is about 18 inches long.   (You need to Login or Register That would make the front and back mount for a 17 ft canoe 18 inches apart.  That is not good. Thule makes bars that are 78 inches long(   (You need to Login or Register ) which is wide enough for your 2 canoes.  You will bang your head a lot on them a lot. They are noisy.
I installed some roof rails like the Surco Roof Rail and have Thule on top of that.  I bought the Thule equivalent on the Surco and found then flimsy.   (You need to Login or Register To install these holes must be drilled in the roof and I could not find any guide as to where wires and other things were in the roof. I have the shorter Thule bars and when I want to hall 2 canoes I put a 1X4 on top of the Thule bars and attach it with SS hose clamps.  The rope that holds the canoe down also goes around the Thule bars.