These are ambush predators that stay/float vertically, head down among vegetation pretending to be a twig or a plant and wait for a suitable prey to come by too close.
Young Sorubim species like the company of each other; adults don't care.
IME and IMO, chances are great that yours is S. elongatus, which tops out at 1', not 2' as S. lima does. They are quite hard to tell apart from the exterior features for laymen like us:
http://www.planetcatfish.com/forum/viewtopic.php?f=13&t=30938&hilit=+elongatus (that's one of mine I was trying hard to ID)
I've never seen a 2' one in person, not even one longer than 11"-12" TL, while I have owned and seen scores of them. This leads me to believe that most/almost all we have in the US are elongatus. I have seen only 1 or 2 approximately two-footers on the photos originating from the USA here on MFK and a few in between 1' and 2'. Our colleagues in Europe say they see 2'-ers sometimes, not seldom.
IDK about Canada. Are there any Canadians with relevant experience here?
http://www.planetcatfish.com/common/species.php?species_id=697 offers kind of soft ID: "...Very generally, Sorubim with spots are usually S. elongatus. (TBTB edit: as opposed to the other 4 species in this genus; this appears mostly true IME with ~20 of these fish.) They are more of a black water species and, as with most such species, tend towards more variable, spotted patterning."
They need not live feedings, unless we are talking earth worms or ghost shrimp, lizards, land frogs, etc. They are small predators that snatch small fish (anything that can fit in their mouth which is relatively and surprisingly big for their slender body structure but not that big compared to other medium and large pimelodidae catfish), crustaceans, insects in the wild. I always feed mine frozen/thawed foods - small whole fishes, fish pieces, shrimp/prawn/etc. or their pieces if too large (do not peel; raw is better than cooked), and sea foods.
They can be trained to take pellets but the cases where they thrive on pellets are very few it appears to me, even on Hikari Mascivore pellets. I have never seen them fat and happy on pellets, rather always thin and slow-growing. Anyone, correct me, please, if your experience differs.
When small mine like freeze-dried and fresh bloodworms, plankton (mini-shrimp-like creatures), etc.
The growth on elongatus is not fast, perhaps 6"-7" in one year starting from ~3". As you see my experience with lima is most likely zero, so IDK how fast they grow. The fact that they reach 2x larger adult size may or may not matter.