The thing you've got to keep in mind is the plecos diet. Alot of the plecos that reach the size you're looking for are vegetarian, and putting them in a tank with carnivores can prove fatal (I.e a high protein diet for these fish causes bloat, and ultimately death). So stay away from any of the panaques (royals, blue eye, etc).
The coolest, carnivorous plecos (those from the pseudacanthicus genus), like L24, L25 and L600 reach sizes like what you're looking for, but finding one that size in Canada is impossible. And if it was possible, they'd cost you near the price of a nice BD. L114 is the most affordable of the pseudas. You don't really see them on the Canadian market at that size either. Whenever you see plecos kept with rays on Asian set ups, they're almost always pseudas.
One suitable pleco for your tankmates and tank size would be an acanthicus Adonis. True monsters, they can apparently reach over 3 feet, and their guts can handle the higher protein they're sure to get in your tank. If you want something extra special, a big albino Adonis would be a true show pleco.
