Yeah, you're definitely stuck with that canopy going with t-5 lighting. I went with a suspended canopy look, rather than going for an on-tank option, and I feel it looked pretty good. You could also have a look at TJ's tank sometime, as his inspired mine, and probably executed it better...although his wasn't a canopy, just pendents.
I will say that Metal Halide is probably cheaper equipment-wise to set up...but will run a lot hotter and would, as noted, require you to sacrifice the canopy. On a related note, with t-12 lighting, I'm uncertain how much help that tin foil is giving you. The bulbs in VHO's have internal reflectors that send most of it downwards to begin with.