partypoker.ON is the Ontario-licensed, ring-fenced skin of partypoker, regulated separately under iGaming Ontario and not connected to the international partypoker/iPoker liquidity.
Traffic is lighter than GGPoker.ON simply because the overall player base is smaller, but the games that do run tend to be soft — weaker regulars than you'd typically find in Europe, and the whales who do show up are usually significant.
Like the rest of the partypoker family, HUDs and tracking software are banned at the tables — nobody can see your stats, and you can't see theirs, which changes how exploitable aggressive lines are compared to a HUD-legal room.