Ah, OK. Now it's clear regarding the area you are talking about. I haven't done it - and I can't exactly remember it ever being talked about here on this forum - but hopefully there will be someone out there that can help. In lieu of that...
-- Have you measured the backrests on a Canyon? Maybe go to a local dealer if need. Will they physically fit? That would be the first thing I would check.
-- Where they ever an original option on the Bimini? Check that avenue, as well.
-- Will you have any clearance issues when opening the lids? Will they still open far enough for you? By "fold out"... do you mean they fold "up" because the top edge is on a hinge? Will you have to do the same thing to be able to open the lid?
Those are things you can easily check on, yourself.
If buying the Canyon backrests doesn't work out, then you'd be looking at having them custom made. Which, most likely, would be less expensive, anyways. Either using a piano hinge on the top edge, or the typical 'slide into place on clips' that a lot of back rests are secured with. All of that should be pretty straight forward for an upholsterer with boat experience.
I'm assuming the vertical distance for the mounting of the backrest isn't very big? If so, google "coaming pads". Just another idea there... whether actual pads or glue-on foam mat.