Technically, you can corn/smoke any cut of beef. I've done beef ribs, cross rib roast, eye of round, and blade roast.
I think brisket was traditionally used (as Montreal smoked meat) as its plenty tough and the long smoking/steaming times help with tenderness.
Still, when going for Montreal smoked meat (MSM), you will miss the texture and fat ratio thats available with brisket. So it may be somewhat hard to find, but the results are generally worth it.
I usually order my brisket from Joe at Fairmont butchers
3833 St-Laurent, 514-288-8046
Ifn you want to experiment with MSM maybe have a looky here