I have an old Electric furnace that I can mix and match elements to get almost any load. but it's awkward and ugly. Great for initial tests. (Seems my Onan, rated at 12 KW won't quite do that!) But not very conveniant for periodic tests.
One Big Generator guy in South Western Ontario bought a surplus load bank from the Federal government. It was a Van Body full of toasters! I can just see the Gov employee with his Gov credit card walking into Walmart, asking for a hundred toasters.! That would be about 150 KW in load.