You would need to use an acrylic heater and bend the acrylic to that radius.....To make the canopy fit, there are several ways I could see doing it making it sit on the tank.....1 way would be to route a dado on the inside where the canopy would sit on the tank before bending....The other option way I'm thinking is glue a strip/support inside the acrylic piece that would act as your lip for the canopy to sit on the tank, but either way the 2 methods would have to be done before the piece is bent....
I'm assuming....but it appears the tank is cylindrical or pretty close......I wouldn't leave the back open.....Just me, but I would seam it using WeldOn 40. Once the seam is complete and sanded and buffed you would have a hard time telling were it was seamed......A bit of work, but worth it......