Hi
In terms of adjusting while visiting ..you can't go in with that intention, if they feel you came in with that plan they will refuse the i485. Now people do, but it's only supposed to be if "circumstances changed". I'd talk to a lawyer about that.
With TN, it's not a dual intent visa, it is strictly temporary. When you apply for TN you can't have immigrant intent. You will need to show you will go back to Canada. It is up to the officer, but I think a TN would be hard to get with an immigrant visa in process.
When you apply for a TN they send you to the back where they can see your consular visa applications. If they see you have a immigrant visa in process, they can conclude you won't come back. Again, it's up to the officer.
Now if you did get a TN, you can adjust, but I'd talk to a lawyer to be extra safe.
In terms of L1, it's flexible, it is dual intent. It's ok to want to immigrate, it's ok to adjust when coming in on an L1. You can even use your approved I130 to adjust from an L1, you don't need an approved I140.