Ok, I will break this down properly.
First, it isn't going to be a Secret or Extra level. They would show these openly.
It cannot be in world 6. These leves are all to... ORANGE and dark to be close to 1-7.
It cannot be World 5. These levels are all in the air. Too far away from 1-7. (Maybe 5-5? ... Na.)
Once again, World 4 is too orange. Can't be.
World 3? Maybe. It isn't:
3-2: You said it wasn't.
3-3: Too much water.
3-4: Fort level.
3-5: In the trees. There are no tress in 1-7 like these.
3-6: Cave level
3-7: Too much water.
3-8: Castle level.
World 2:
2-1: Too much forest in the background
2-2: This has the "bright" level background like in 1-1. If you confuse this with the dark jungle background of 1-7... you really don't now much.
2-3: You said this wasn't it, either.
2-4: Fort level.
2-5: Too much air in this level.
2-6: Cave level (Notice a lot of the x-6 levels are cave levels? Or at least have SOME underground area? All but 5-6, actually.)
2-7: Not nearly open enough to be mistaken for 1-7.
2-8: Castle level.
World 1:
1-1: Too bright. (See 2-2 comment)
1-2: Too open.
1-3: Cave level.
1-4: Fort level
1-5: Self scroller.
1-6: Like 1-1, again.
1-7: Ok, this is the level in question.
1-8: Castle level.
What have we done here?
Well, I've eliminated all levels but 3-1. And I really don't think that is it either. Maybe that part in 3-1 with the vertical wodden platforms that Yoshi can go up through? There's something like that in 1-7. The only other alternate is that it is a bonus area that strays from the main path of a level. I'll have to think about these paths for a while before I can come up with anything better.
Or I can actually SEE the commercial. You show me ANY screenshot of ANY level of SMA3, and I'll be able to name it.
Something doesn't seem right here. I'll have to see the commercial. Maybe. Or make random guesses. (These aren't that random. I am examining the levels in my mind to see if I can find ANY part that is similar enough to 1-7 to be mistaken for it.)
Everyone has their own opinions, no matter how WRONG they are.