I found a small list of Large Fish you could possibly use. It gives a little description of each and may be helpful. For pics use google images.
The more educated MFKers can correct any info that may be inaccurate. I did not write it I just found it.
Also keep in mind some of these monsters may be illegal so look into it before you decide (not sure about canada).
The Cast of Characters
Here are a few of the more popular "big fish", with some brief notes.
Oscars (Astronotus ocellatus) are the quintessential "big fish", they're actually much less aggressive than their reputation, and often take a beating from other large cichlids.
Red Devils (Cichlasoma labiatum) basically hate everybody, and declare about 100 gallons of space as their territory. They make great solo fish, but generally need huge tanks to have any chance at compatibility.
Snakeheads (Channa sp.) are very powerful predators that want to be alone, and require a huge tank to attempt to mix with others. They are sometimes blamed for actually breaking the glass of an aquarium.
Arowanas (Osteoglossum bicirrhosum) are very bizarre and attractive in appearance, but can get 3 feet long and are prone to flying out of the tank in panic. They are also relatively peaceful with fish near their size, and vulnerable to attck by more aggressive species.
Clown Knives (Notopterus chitala) are not terribly aggressive, and are again prone to being attacked by some of the more assertive species. They generally prefer live foods, and sometimes accept frozen.
Pacus (Myleus sp.) are the big cousin to the piranha family, and can get to 50 pounds or more. They eat mostly plant material in nature, but will happily accept nearly anything that fits in their mouths.
True Gouramis (Osphronemus goramy) are not very aggressive for their size, and eat most foods readily.
Redtail Catfish (Phractocephalus hemiolopterus) get too large for any tank less than 1000 gallons, and greedily gulp down any other fish that fit in their mouths. They are very prone to a deadly skin condition if kept in too small an aquarium.
Channel Catfish (Ictalurus punctatus) also get quite large and require very large quarters (like the Mississippi River). They tolerate crowding better than some other large catfish, but seem to compensate by attempting to skin other fish in the tank.
Shovelnose Cats (Sorubim and Pseudoplatystoma sp.) are generally quite hardy, and not very likely to be picked on. They range in size from about 18 inches for the common lima species to over three feet on the tigers, but all have huge mouths capable of gulping down fish over half their size.
Tinfoil Barbs (Barbodes schwanenfeldii) are often fast enough and unrelated enough to mix fairly well with more aggressive species. They eat prepared foods readily and are generally very hardy.
Iridescent Sharks (Pangasius sp.) can get up to three feet long, but are very vulnerable to attack by even some of the less aggressive species, often losing eyes or finnage. They are also quite active and require quite a bit of swimming room.
Silver Dollars (Metynnis and Myleus sp.) are also quite active and different enough that they tend to mix fairly well. There are a number of species, some of which do not get large enough for this application. The Red Hook is a particularly attractive species that gets over 12 inches long.
Lyretail Plecostomus (Hypsotomus plecostomus) - the common one sold as algae eating fish - can grow to be several feet in length. Their heavy armor makes them almost invulnerable to attack by all but the most aggressive species